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Table of Contents
Are all air compressor pressure switches the same?
While all pressure switches have the same purpose (switch on or off at a certain pressure), pressure switches come in a lot of different design and types. Some are very basic and not adjustable, while other are very flexible or have extra options.
How does a compressor pressure switch work?
Air compressor pressure switches use air lines to monitor pressurized air as it moves to and from your air tank. All pressure switches have an element that reacts when pressure is applied to it. The most common device is a diaphragm that will deform or compress when exposed to pressurized air.
Are air compressor pressure switches Universal?
This is a pressure switch, control valve with a single port connection manifold. The switch is a universal pressure switch replacement, convenient to replace the broken one.
Can you fix a pressure switch?
Because it gets so much constant use, the pressure switch is the most common failure point for a well pump. Fortunately, it is also easy to repair and replace.
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When a well pump fails, the problem can often be traced back to one part – the pressure switch. This above-ground part near the pressure tank is responsible for turning the pump on and off by monitoring the pressure in the system. The pressure switch consists of an internal spring mechanism connected by electrical contacts and turns the pump on when the system pressure falls to the minimum pressure setting and then turns the system off when the pressure reaches the maximum setting. This switch works properly and keeps the home’s water supply at the faucets at a steady pressure.
Because it is so commonly used, the pressure switch is the most common point of failure for a well pump. Luckily, it’s also easy to repair and replace.
before you start
Pressure switches are typically available in three pressure ranges: 20 to 40 psi, 30 to 50 psi, and 40 to 60 psi. Make sure you buy a new switch that matches the old one – the rating is usually printed on the switch body.
safety aspects
The current flows through the pressure switch of your well pump. Before repairing, replacing, or even inspecting the switch in its housing, make sure that power to the pump is turned off at the electrical service panel. After removing the switch’s outer casing, use a voltage tester again to check for power. Also, wear eye protection when working on your well pump pressure switch.
What would cause a air compressor not to shut off?
A faulty pressure switch, a check valve that has malfunctioned, and leaks are the most common causes of an air compressor failing to shut off. Other things worth checking include the gauge and the intake valve. Also, remember that even the motor could be having problems so check it as well.
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In this post, we’re going to look at why your air compressor won’t shut off and some of the best ways to fix the problem.
Read it to the end if you’re trying to fix an air compressor that won’t shut off (just runs and runs).
The air compressor does not turn off – why it happens and what to check
So your air compressor won’t shut off when it’s full?
Well, here are the possible causes and the solutions you should try:
It could be a defective pressure switch
A common culprit is a faulty air-off pressure switch (this switch is designed to shut off the compressor when it reaches the correct pressure), so this is the first thing you should check.
The good thing is that the pressure switch is fairly cheap and also easily replaced (you can buy a replacement pressure switch cheaply on Amazon).
You can usually see it if you take the cover off – the pressure switch is usually connected to the tank and is the part with some wires going into the engine.
Go to YouTube and look for videos on how to replace the air compressor pressure switch if you need help replacing the pressure switch.
Quick tip: Before you order a new pressure switch, try disassembling your device’s pressure switch and thoroughly cleaning both the diaphragm and the hose that goes back to the tank (just to make sure it’s not clogged). It could save you valuable time and money.
It’s probably a defective check valve
Also, the tank check valve may be bad and you may need to replace it.
Now, the check valve tends to loosen or wear out over time.
Once this happens, air can escape, causing your air compressor’s pump to start running constantly to make up for the loss of pressure…
What you do is open the check valve (it’s under the pressure switch)…
There could be something inside that is broken (e.g. a spring), causing a malfunction.
If the pressure switch doesn’t shut off (i.e. the check valve falsely opens), you should replace both of them.
The tank has a leak (possibly)
A leak in the tank can also cause an air compressor to run constantly.
You see, if there’s a leak somewhere in the tank, your air compressor won’t shut off because it only does so when the tank is full (and now it can’t get full because of the leak).
Therefore, examine the tank for signs of a leak and repair it.
The bottom line is, your truck air compressor won’t shut off (it really doesn’t matter what model it is) if something prevents it from reaching full pressure.
The inlet valve may be defective
It could even be a bad intake valve that is the cause of the problem.
You see, the inlet valve (also called the regulator valve because it acts as a regulator for the air that enters the unit and is compressed in the air tank) is known to wear out fairly quickly.
And when it does, your air compressor will start working for the simple reason that the pump will struggle to put in enough air to properly pressurize (and keep) the tank.
This will result in the pump not switching off.
Remember that intake valves are dirt cheap (check prices on Amazon) and very easy to replace.
You are probably looking for a faulty gauge
On some models, particularly Dewalt air compressors, a common cause of failure is a malfunctioning gauge (located on the air tank).
Now, if the gauge isn’t working properly – and this is mainly due to corrosion – the pressure is likely being read incorrectly, preventing your compressor from starting when the intended cut-out setting is reached.
Solution?
Well, you may need to install a replacement air tank gauge.
Other probable causes
Don’t forget that there are many gaskets (mechanical seals) there that could loosen or crack, causing leakage. Therefore, look for leaking seals.
Unfortunately, they’re not that easy to spot – however, a soap test should help you spot leaks (do it and see if it reveals leaky seals).
Also, there are a few other parts that keep causing the problem, including the engine failing (the engine itself may be dead!).
Also, the performance of your air compressor can be affected by dirt and grime that has gradually built up inside during normal use.
As a result, pump performance suffers and it can start to keep running.
Your first step here is to replace the air filters – and you should do this regularly to avoid problems.
The last thing you need to know is that your air compressor may be underpowered because you’re using the wrong extension cord.
Our recommendation is to switch to a sufficiently powerful extension cord (or plug it in directly).
It’s worth noting that most manufacturers specifically advise against using extension cords with air compressors.
last words
A faulty pressure switch, a faulty check valve, and leaks are the most common causes of an air compressor not shutting off.
Other things worth checking are the gauge and intake valve.
Also keep in mind that even the engine could have problems, so check it out as well.
If the above doesn’t fix the problem, you may need to consider listing your air compressor for sale on Craiglist (or other second hand sites) and hope you find someone to buy it. Otherwise you could end up losing a lot of cash.
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What is the purpose of pressure switch?
Pressure switches are widely used for a large range of applications throughout industry and manufacturing. Their function is to provide systems with electrical feedback in response to measuring a rise or fall in pressure. A pressure switch is usually adjustable with regard to the chosen set point of operation.
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About our pressure switch product range
Pressure switches are widely used in a variety of industrial and manufacturing applications. Their function is to provide systems with electrical feedback in response to sensing an increase or decrease in pressure. A pressure switch is usually adjustable with regard to the selected switching point.
Also known as pressure sensors, they are used to respond to fluid pressure. For example, a pneumatic switch in compressors and pumps or hydraulic switches in automotive engineering.
As a leader in the industry, Applications Engineering specializes in providing products for a variety of measurement applications. For simple surveillance systems we offer single pole double throw switches while for more complicated and advanced needs we offer a range of single pole double throw switches.
Depending on the application of the pressure switch, we can offer different models that best suit your needs. Whichever of our switches you choose, you can be sure that it will respond quickly, reliably and consistently, whatever its function.
We supply to a variety of companies and businesses with a wide range of needs. This can include anything from highly robust and accurate electronic pressure switches to differential pressure switches. If you’re not sure which product is best for you, don’t hesitate to contact us today. You can speak to a member of the team who can give you expert advice and guidance.
Each of our pressure switches are manufactured to the highest standards. This makes them robust, reliable and durable. They have undergone rigorous and extensive safety testing and are available at extremely competitive prices. Please browse our product range for more details.
What are two types of pressure switches?
There are two different types of pressure switches: electromechanical and solid-state.
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Some people will tell you that a pressure sensor is a device used to measure the pressure of a gas or liquid. In addition to pressure switches, this category of pressure sensors also includes pressure converters, pressure transmitters and pressure transmitters.
Are pressure switches interchangeable?
Different furnaces may have different types of pressure switches in them. Based on the size of the unit (meaning heat output capability, not the physical dimensions), the amount of suction the pressure switch requires to work will vary.
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The pressure switch in an oven detects proper ventilation of the device.
Why doesn’t my oven light up?
I get this question from readers a lot, and while there are several possibilities, they usually think the igniter or gas valve is failing. While this is a reasonable suspicion as to the cause of the fault, there is one that is often overlooked because it is not understood: the pressure switch.
Let’s take a closer look at this part, what it does, how it works and what its purpose is so you might be able to figure out if the pressure switch is your problem and if your oven ever won’t light what you can do to fix it .
Or maybe you understand why that flashing red light indicates the pressure switch is open and yet it might not be the problem.
What does a pressure switch do?
A pressure switch is a fairly simple component. Like all switches, it makes a connection to allow current to flow through. Think of all the switches like a drawbridge, but instead of cars, electricity is waiting to drive across it. When the bridge is open, nothing goes across it, but once it’s closed, traffic can pass.
In the case of a light switch, no lights will come on until you manually flip the switch and power the light. However, your pressure switch is activated by air pressure, or in this case suction. The suction pressure that your oven’s pressure switch needs to function is generated by the suction fan or induced draft. When this fan turns on, it pulls a vacuum into the pressure switch through the rubber hose you see that connects the two, which then pulls the switch into a closed (connects) circuit to allow power to flow to the next component, which is the igniter .
The pressure switch is connected to the housing of the suction fan. Image of a pressure switch wired to the exhaust fan housing on an oven.
The purpose of your oven’s pressure switch
The pressure switch in your oven serves as a safety mechanism. It is there to confirm that the unit is drawing correctly. If the device doesn’t pull properly, it doesn’t work as efficiently and poses a safety hazard because it doesn’t remove unwanted gases that can make us sick or cause small explosions in the heat exchanger. Therefore, if the pressure switch is not satisfied with the correct suction power, it will not allow the device to fire.
What is a high pressure switch?
Different ovens may contain different types of pressure switches. Depending on the size of the device (i.e. heat output, not physical dimensions), the amount of suction the pressure switch needs to function will vary. But when it comes to high and low pressure switches, it usually has to do with the number of stages a unit can operate in.
While many of us still have a single stage oven that runs at full capacity every time it is turned on, there are two stage units that run at a lower heat output and then switch to a 2nd stage for more heat when needed. These types of stoves require a dual pressure switch so they can monitor one level of suction on a low flame and then another on a high flame as they require different amounts of ventilation to function properly.
Some two-stage ovens use what is known as a pancake switch because the two pressure switches are “pancaked” together, while others have two separate pressure switches. In any case, one of these switches is called the low pressure switch and the other is called the high pressure switch.
This is what a “pancake” type push button switch looks like and if you need to replace it just replace both of them as you will probably need to buy it that way. 1/2
Causes of pressure switch failures
Bad/Shorted Switch Vacuum fan runs too slow Vacuum fan motor is bad Blockage in vacuum fan Blockage in chimney/crack/hole in vacuum tube Bad/loose wiring connection Water build-up in vacuum fan housing (Heavy Duty Ovens) Loose vacuum tube
A pressure switch can be tricky… This part is finicky so it can fail and then work again, making it difficult to locate. A downward flow of air can cause a temporary failure. A “tired” switch may not work today and tonight, then again tomorrow. Intermittent failures are more difficult to diagnose, so watching and listening to the unit running or running it can help pinpoint your problem.
What to do if your pressure switch fails?
The table above gives you some causes of pressure switch failure that can be easily confirmed or eliminated as a problem, either audibly or visually. You should start by checking these things as they are the easiest, don’t require any special tools and don’t cost anything.
First, when the device starts trying to run (that is, after the inducer has run for 10-30 seconds), do you hear the gas valve “click” as it opens? The gas valve won’t open if the pressure switch isn’t working, so the “click” sound when the gas valve opens tells us that the pressure switch is fine and the igniter is probably our problem, as we should also note that it isn’t tried and light just before the “click” we heard. If we don’t hear the click…
Listen for a rattle in the suction fan. If so, see if you can remove it. (Make sure you turn off the power first). If you hear the motor whine, grind, or seem to run slowly, you may need to replace it and the switch is probably doing what it’s supposed to do.
If you hear the motor whine, grind, or seem to run slowly, you may need to replace it and the switch is probably doing what it’s supposed to do. Check to make sure the switch hose is tight and intact. If it’s loose, try tightening it a little, and if it has tears or a hole, see if you can seal it or cut away the torn material and reconnect. Be careful as the inducer housing may be hot if the unit has been running recently. Again this would show that the switch is doing its job and it should work now that the hose is attached.
Look for visible blockages in the flue. If one is found, remove it and your problem should be resolved.
If you’ve taken a few minutes to rule these things out and you’re still having an issue, we can confirm that the switch is bad by testing the circuit with a voltmeter and perhaps running the unit for a little heat, at least temporarily get going.
If you have a voltmeter, turn off the power to the device. Remove the wires from the pressure switch and check the resistance (ohms) between the two terminals. If it reads “0” (or close to) then the switch is closed when it shouldn’t be (shorted or stuck). If it measures “infinity” (O.L.), the switch is not shorted and might just be stuck open. In any case, we need to replace the switch, but maybe we can still get it to work temporarily and turn the heating back on for a while. In order to do this…
Remove the hose from the inductor body (carefully as the inductor body may be hot if the unit has been running recently) and gently suck and blow on its end. You should be able to hear the switch opening and closing. Do this a few times and then reconnect the tube to the inductor body and see if it works.
Sometimes the switch gets stuck and just needs a little help releasing it. Even if this works, replace the switch soon. There’s a good chance the switch will get stuck again and it’s always better to fix it on your terms than at the usually awkward time of it failing again.
Voltmeter shows resistance which means our pressure switch is closed and since there is no vacuum it shouldn’t be and therefore has a short circuit. 1/2
Replacement of a pressure switch
The actual work of replacing a pressure switch is fairly easy and doesn’t require any special tools that you probably don’t have lying around the house.
Turn off the device
Disconnect the wires from the switch
Disconnect the hose from the switch
Remove the switch from the bracket (or from the bracket if your new one already has it mounted)
Fasten the new switch back in place
Reconnect the hose to the switch
Reconnect the wires to the switch
See how easy this is?
How much does a pressure switch cost? A single stage pressure switch, whether factory or universal, can range from $20 to $50, while pressure switches for a two stage unit can range from $30 to $75.
Find and purchase a replacement pressure switch
Like many oven components, the pressure switch is not an item typically found in the “big box” stores like Lowe’s and Home Depot. To find a replacement, you’ll likely need to do one of two things: contact the builder that sells your brand of stove, or get a universal replacement from a builder or online.
Ovens are similar to cars and have brand specific parts. So if you want a direct factory replacement, you need to find the supplier that carries your brand. It’s a “don’t call a Chevy dealer for Ford parts” sort of thing. Once you’ve found the supplier that carries your brand, be prepared to tell them what part you’re looking for and have your device’s model and serial number ready so they can help you. However, many of these suppliers are “contractors only” and will not sell to the general public. So the more prepared you are, the more likely you are to get them to sell to you, or at least give you a part number so you can search for it online.
However, a universal pressure switch may be easier to find and purchase at any utility or online. I keep this universal NS2 pressure switch handy so if my or a family member’s unit fails at an inconvenient time I can make the repair without having to hunt for one. These are nice because they handle single and double stage units and can be set to different pressures. They also include brackets that allow mounting in more than one unit. The instructions will walk you through the process of setting up the switch to meet the needs of your device.
NS2 universal pressure switch 1 / 2
You’re not alone
I hope the information I have given you regarding your oven’s pressure switch has helped you to deduce whether the pressure switch is the problem you are having or if another part was the cause. If you’re still not sure what’s going on, I recommend contacting a technician. We don’t want to make things worse or hit ourselves over the head. Remember, we’re in this together.
This article is accurate and truthful to the best of the author’s knowledge. The content is for informational or entertainment purposes only and is not a substitute for personal or professional advice on any business, financial, legal or technical matter.
Answer questions
Question: My vent pressure switch is working properly. I have already replaced the igniter. Is the oven control module my next step?
Answer: It doesn’t really work that way. While swapping parts will eventually get you there and maybe even save you money, you’ll have to figure out where the failure is occurring in the cycle or test the circuits with a voltmeter.
© 2018 Dan Reed
Michael Thomson on August 23, 2020:
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John Monty on June 02, 2020:
this article about the PRESSURE SWITCH… the best and simplest explanation. Well done
Denny on February 04, 2020:
I have 2 pressure switches. A.40 and a
.80 which hose is connected to the induction motor?
Goodajj on January 24, 2020:
The thermostat is calling for heat and the control board says there is a problem with the pressure switch. I disconnect the hose from the nipple on the induction motor and the induction motor starts running, I plug the hose back in and the system works as expected. Any idea what the problem is?
Many Thanks,
Jeff
Kapilan on 11/14/2019:
Hey, so pancake double button switch. When I disconnected the high side hose the stove works, but when I disconnected both hoses it gives me Error 229 Ignition on high flame.
Lennox oven. EL26uh070
Michael on 11/14/2019:
Dan, thanks for this article. It is very helpful. The problem I’m having is that my device is flashing the code that says my pressure switch is closed. As soon as I disconnect (and immediately reconnect) the wiring to the pressure switch, this code stops flashing, the igniter starts, the natural gas comes through and we have heat. The heater runs until the temperature reaches the desired setting, which I set on our thermostat. However, when the temperature in the room drops again, the same pressure switch code will start flashing and the only way to get the heater working again is to disconnect the wiring to the pressure switch. I bought and installed a new pressure switch today but the same problem persists… Thoughts?
Daniel on March 16, 2019:
Does it matter which wire goes where when replacing a pressure switch on a Rudd Silhouette heater unit?
Rick on March 08, 2019:
How do you determine the correct pressure switch for your oven if there is no vacuum rating on the switch? Using the wrong one (e.g. universal) can be dangerous!
Tyler Watson on January 13, 2019:
I have a 100,000 btu two stage Goodman oven. I’ve had people try to fix the issue multiple times but no one seems to figure it out. It starts. ignites. Then it turns off after 5-30 seconds. Do it three times and then wait a while before trying again. The kicker is that it doesn’t always do that. Last year and so far this year it doesn’t start until halfway through winter. However. It chooses its own days when it decides not to work. It will work perfectly for 2-15 days and then have a bad day. And sometimes it only does that for a few hours and sometimes it tries to start and fails for 24 hours. I was just wondering if you encountered such problems. When I take off the top half there is a lot of water there. I don’t know if that has anything to do with it. The flame sensor is good. I swapped the low pressure and high pressure switches. I am in the process of purchasing and replacing the other pressure switch. But if that doesn’t work, you have some advice on where to look next. The codes it throws don’t exist in the manual or online. So I guess. Any advice would be very welcome. Many thanks.
Dan Reed (author) on October 16, 2018:
Patrick – I’m not sure, other than maybe the switch itself is defective. I think you have a boiler here and unfortunately I’m not as familiar with them as I am with forced air systems. Sorry I’m not of much help.
PATRICK GILLESPIE on October 15, 2018:
I’ve searched everywhere for someone who had the same problem as me but can’t seem to find anything so thought I’d report back. I have a Weil-McLain GV-6 and just attempted to start it for the first time this year. The induction motor starts, then the pressure switch circuit closes, then I hear the burner ignite and the burner flame indicator comes on. The burner is only on for a few seconds, then the pressure switch circuit opens again and the system shuts down. I have checked all the wiring and hose connections to the injector body and pressure switch. I disconnected the breather pipe on the exhaust and everything is clear. Do you have any thoughts as to why the system loses vacuum once the flame is lit?
What is a 4 port pressure switch?
This pressure switch features a fixed differential, an actuated diaphragm, and contacts designed to open with rising pressure. It is designed to control electrically driven air compressors and pumps.
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This pressure switch features a fixed differential, actuated diaphragm, and contacts designed to open with increasing pressure. It is designed to control electrically powered air compressors and pumps.
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This pressure switch features a fixed differential, actuated diaphragm, and contacts designed to open with increasing pressure. It is designed to control electrically powered air compressors and pumps.
This pressure switch features a fixed differential, actuated diaphragm, and contacts designed to open with increasing pressure. It is designed to control electrically powered air compressors and pumps.
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How To Replace An Air Compressor Pressure Switch.
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Air pressure switch models and options
Air Pressure Switch Models and Options, a perfect pressure switch for every application.
While all pressure switches have the same purpose (to turn on or off at a given pressure), pressure switches come in many different styles and types.
Some are very basic and non-adjustable, while others are very flexible or have additional options. So what types of pressure switches are there? Here is a basic overview of the different models and options available.
Note that this is not an or-or list, but an and-and list.
Most pressure switches, especially on air compressors, have more than the following.
On / Off / Auto setting
Some pressure switches have an on/off or an auto/off switch. Most of the time this is basically the same (the wording depends on the manufacturer).
When you press “on” or “auto”, the compressor will start and stop automatically according to the set pressure setpoints.
If you press Off, the setpoints are ignored and the compressor shuts off.
Air compressor pressure switch with OFF/AUTO selection
This is basically an all in one solution for small compressors.
This type is mainly found on smaller (piston) air compressors where the motor is started and stopped directly by the electrical contacts of the pressure switch (see also “Electrical contacts” further down this page).
Many pressure switches do not have an “on/auto/off” switch. It is always in “Auto” mode, opening and closing its electrical contacts depending on the pressure.
This type is typically seen on larger air compressors where the electric motor is started and stopped by external relays/contactors or motor starters.
Electrical Contacts / Rating
Inside the pressure switch there are 1 or more electrical contacts that open and close depending on the pressure. The number and rating (size) of these contacts will vary.
Some pressure switches are able to switch the electric motor on and off directly.
Other pressure switches can only turn on and off a small control signal.
The control signal is then fed to the central controller or used directly to switch large contactors or motor starters on and off.
Direct motor switching pressure switches are only seen on smaller air compressors with relatively small motors, say up to 10 kW (about 13 hp).
The rated power of the pressure switch must exceed the rated power of the compressor motor!
Then there are 3-phase and 1-phase models. 3-phase pressure switches have 3 separate contacts for 3-phase motors. 1-phase models have only 1 set of contacts, for 1-phase motors or for low current control signals to the main controller (on large air compressors).
Electrical connections on a single-phase pressure switch.
pressure setpoints
The pressure setpoints are the pressure values at which the pressure switches will change from “on” to “off” and vice versa. These points are also called switch-on and switch-off points.
Most pressure switches on air compressors are set to open (turn off) at around 7 bar and close (turn on) at around 5.5 bar. The difference between the lower and upper setpoint is called the pressure band or pressure difference.
With regard to pressure setpoints, we can divide pressure switches into the following groups:
– Both the upper and the lower setpoint can be set individually
– Only the upper set point can be set/changed and the lower set point follows automatically at a set distance (fixed pressure difference).
– Both the upper and lower setpoints are factory set and cannot be changed.
For more information, see our Setting up your pressure switch page.
Also make sure that the maximum pressure rating of your pressure switch exceeds your maximum compressed air pressure.
Most pressure switches only go up to 8 or 9 bar (125psi) which is pretty much useless if you have a 13 or even 30 bar compressor.
mechanical connection
Some pressure switches are designed for mounting directly on a tank, others for installation in a control cabinet and are connected to the compressed air system via hoses.
The physical port where the compressed air connects to the pressure switch is often referred to as a “port type”, “port type” or “flange type”.
The most commonly used sizes/types are 1/4″, 3/8″ or 1/2″ NPT female threads.
Some pressure switches only have 1 port, others have multiple ports of different sizes so there is always one that fits your compressor.
Compressed air connection at the bottom of the pressure switch
Pressure switches with integrated relief valve (see below) have an additional relief connection.
Integrated or optional drain valve
On the smaller reciprocating compressors (home shop/garage) a relief valve/relief valve is used to relieve air pressure from the compressor discharge line for easy starting.
It vents any pressure in the line between the compressor and receiver when the compressor stops
This drain valve is usually integrated or attached to the pressure switch.
Sometimes it is fixed in the pressure switch, but most often the relief valve is optional and there is a reserved mounting location on the bottom or side of the pressure switch.
Pressure switch with connection point for drain/relief valve.
Blow-off/relief valve installed on pressure switch.
However, many pressure switches do not have an integrated or optional relief valve. So if you need one on your compressor, pay extra attention.
The drain valve, when installed, is operated by a small lever inside the pressure switch.
The lever opens the relief valve when the cut-off pressure is reached and the compressor stops. See our Air Compressor Unloading page for more information.
If you are interested in buying a pressure switch, visit my buy pressure switch page.
What Is an Air Compressor Pump?
The Air Compressor Pressure Switch measures the pressure in your air tank and shuts off your compressor when it reaches the required air pressure.
The air compressor pressure switch also helps your machine maintain the correct level of pressure while you go about your work. The switch can turn on your compressor when tank air pressure drops and more air is needed.
This makes your air compressor pressure switch a part that gets a lot of use and therefore may wear out faster than others. You should maintain it properly and repair or replace it if there is any problem. The switch is your best defense against over-pressurizing your compressor’s tank and air lines, keeping you safe from breakage and danger.
So let’s discuss what an air compressor pressure switch is and how it will work for you.
How does an air compressor pressure switch work?
Air compressor pressure switches use air lines to monitor the compressed air as it moves to and from your air tank. All pressure switches have an element that responds to pressure. The most common device is a diaphragm that deforms or compresses when exposed to pressurized air.
The air pressure in your compressor tank rises and eventually builds up enough back pressure – also called cut-off pressure – to change the shape of this diaphragm. A deformation here causes a movement in the pressure switch.
When the diaphragm of your air compressor pressure switch is sufficiently deformed, its movement breaks the contact inside the switch, stopping the current flow to the compressor’s motor circuitry, preventing the compressor from further pressurizing the air in your tank.
A constant air pressure at a given volume keeps the diaphragm deformed. If the air pressure in your tank drops enough, the diaphragm will return to its normal shape. Once this pressure – called the cut-in pressure – decreases to a certain level, an internal operator within the diaphragm deforms in the opposite way. This movement closes the circuit and restarts the motor.
Your air compressor pressure switch will continue this dance as long as your machines use compressed air. The cycle is interrupted when the device loses external power or when a problem occurs. Leaks at any point in your compressor’s pressure switch and near the casing can stop your work and cause big problems.
What does your switch look like?
Pushbutton switches often look like a small rectangular box the size of your palm. The case can be plain or have its own switch that allows for multiple positions such as “Auto” functions.
The switch is typically mounted on the reservoir to allow air in the air reservoir to flow freely to the switch. Your pressure switch monitors the air coming out of that compressor tank so you know how much pressure you’re using and can tell if there’s a problem.
Compressed air is pushed in all directions and on all sides of the switch simultaneously, so damage to the housing or reservoir can cause a problem in getting correct readings.
Components of a pressure switch
While there are a few different air compressor switch designs, the typical switch consists of six components:
Pinch: The pressure switch closes or breaks a circuit, telling the air compressor when to turn on. The incoming and outgoing wiring is connected to the pressure switch through the terminals. Contacts: The contacts are two points in the pressure switch that separate and come together to make or break the circuit. They are made of a conductive metal, and when the contacts are separated and the circuit is broken, the air compressor motor shuts off. Diaphragm: A diaphragm, also known as a diaphragm, is a piece of flexible material that moves as the pressure inside the air tank changes. When the pressure increases, the air pushes against this membrane. When the desired pressure is reached, it pulls the conductive contact points apart, breaking the circuit. Pressure Switch Relief Valve: This safety valve is designed to relieve pressure trapped between the pump and the check valve. It is located at the base of the pressure switch control where it is connected to the check valve with nylon or copper tubing. The valve is activated when the contacts separate. Adjustment Springs: A spring allows you to adjust the air compressor’s on and off points. When you tighten the spring, more pressure must be exerted by the diaphragm before the spring forces the contacts apart. When you loosen the spring, it moves with less pressure. Auto/On/Off Lever: Some pressure valves have an Auto/Off or On/Off knob or lever to control the pressure switch. When set to Auto or On, it uses the specified on and off settings to determine when to turn the engine on and off. When it’s off, a piece of plastic wedges between the contacts and blocks power to the motor.
Check your air compressor pressure switch
You can easily test your own air compressor pressure switch with an ohmmeter and a separate air source. Proper testing can save you a lot of time and headaches when repairing the air compressor switch:
Start the testing process by unplugging your air compressor.
Next, unscrew and remove the case from your device.
Disconnect the wire sets that run between your pressure switch and the terminal block. These wires are usually blue or brown.
Be sure to leave the black and white wires connected. These provide power to the switch and can be difficult to replace or cause problems later if you disconnect them.
Locate the valve and apply air to your pressure switch. Be sure to use a source that provides more air pressure than the switch’s current setting. If you don’t apply enough pressure, the switch will not engage.
After air has been applied to the switch, place the leads of your ohmmeter on each of the loose wires.
If the ohmmeter reads “0”, the switch is closed due to the pressure and your switch is working properly.
Your ohmmeter may read open, “OL,” or infinity, which means there may be a problem.
Adjust the pressure switch set point by turning the set point screw counterclockwise. Apply pressure as you do so, making sure the loop closes and the ohmmeter reads ‘0’.
If your meter reading stays open even with the screw fully loosened, the switch needs to be replaced.
This process is slightly different for some units, especially in industrial environments. You have some special requirements for testing and adjusting the setpoint, but the overall elements are the same.
Concerned about the process? Contact a Quincy Compressor Service Representative for help testing or to have your entire compressor serviced.
Changing the print settings
Your pressure switch is designed to turn on when the pressure in the tank is lower than desired and turn off when the required pressure is reached. In order to achieve the pressure you need for the desired application, you must set the cut-off point to the appropriate pressure. You do this by moving the adjustment spring.
When you compress the adjustment spring, it requires more force from the diaphragm to move the contacts. When you decompress the spring, it moves more easily and activates with less force from the diaphragm. You can adjust the tension in the spring by turning a long screw attached to the spring. Turning counter-clockwise relaxes the spring, lowering the cut-off pressure. Turning the screw clockwise compresses the spring and increases the shutoff pressure.
Leaking air compressor switch and repair
Compressor switches often end up leaking after a long period of use. Thankfully, you’ll find that the number one cause of switch leaks is something you can check and fix.
Over time, the diaphragm in the air compressor pressure switch can tear or wear out a hole in it. When this occurs, air blows around the tank and escapes, moving through the diaphragm and out of any opening in the switch housing.
This is probably the scenario you face when you notice leaks originating from unusual places like electrical wire connectors and fasteners. Sometimes you have to remove the cover from the switch to check for leaks, especially if the area near the opening is filled with cable strain reliefs.
If your switch’s relief valve is on the outside of the case, that’s the first place to look for leaks. Air escaping from this valve or near its port on the cover usually indicates a puncture or other problem with the diaphragm.
These types of leaks can be difficult for many people to fix. Sometimes problems arise in obtaining the correct diaphragm replacement. Customers have also encountered concerns with parts or new problems after disassembling and reassembling their air compressor pressure switch.
Depending on the cost, you may be able to save money and hassle by replacing the pressure switch. Buy a new switch and you can expect a longer life from your air compressor as you get a new diaphragm, tips and other parts that wear out over time.
Get to know the relief valve
Concerned that you have a relief valve problem and that the air compressor pressure switch is leaking? Let’s take a look at the relief valve itself and see what its leaks can look like.
The relief valve is a needle valve that monitors your pressure switch and responds to pressure switch movements. It activates and opens when the compressor motor shuts down, creating that telltale hiss that is present in any properly working air compressor.
The relief valve opens, allowing the compressor air trapped around the compressor piston to escape to keep everything in good working order.
You can tell air is escaping from this valve when the hissing continues for more than a few seconds or when you feel a steady stream of pressurized air at the bottom of the valve. Sometimes these relief valves just need cleaning, although a major crack or deformation means they need to be replaced.
Breaking the Duty Cycle
Some air compressors have a 100 percent duty cycle, which means they can be used continuously and will not overheat. These high performance models are designed to prevent engine damage from constant use. Other compressor systems have a limited duty cycle, so prolonged use may damage the unit.
Failure to adhere to a limited duty cycle can result in significant overheating and damage to your air compressor. Not only does the damage threaten the engine, but the heat can cause an air compressor pressure switch to leak if friction is caused or the heat generated is localized near your pressure switch.
This type of problem is common when workers use two compressors with a single compressor tank. These dynamics change the workload of each compressor. If you are using this setup and are unsure how to adjust operation or replace compressors, contact us today to ensure you are not at risk of major equipment failure.
Replacing your air compressor pressure switch
The most common method of repairing the air compressor pressure switch is to actually replace the device.
Choosing the right air compressor pressure switch starts with learning the pressure requirements of your air compressor. Perhaps the most important thing is to find the manual and determine the cut-in pressure range. Your new switch should operate at the lowest cut-in pressure rating in your range to avoid damage.
For cut-in pressure, aim a little higher and set your device 5psi to 10psi higher than necessary to keep things running smoothly. This buffer gives your air compressor enough time to start working and catch up.
There are also some other items that you should carefully consider when purchasing a replacement pressure switch:
Electrical Load: Make sure your new pressure switch can handle motor currents if you are using a smaller compressor. If you are unsure of the requirements, refer to your manual or contact our staff for assistance.
Make sure your new pressure switch can handle motor currents if you are using a smaller compressor. If you are unsure of the requirements, refer to your manual or contact our staff for assistance. Maximum pressure: Compressors are designed for a specific maximum pressure. Make sure your new switch is rated for that pressure or higher. Also, be careful never to set a pressure setting higher than your compressor or switch can handle.
Compressors are designed for a specific maximum pressure. Make sure your new switch is rated for that pressure or higher. Also, be careful never to set a pressure setting higher than your compressor or switch can handle. The “On” Switch: Does your current pressure switch have an on/off switch? Not all do; Some have the switch on a separate panel. Your replacement must match your original in terms of switches.
Connectors: There are many adapters for pressure switches and their connectors, but it’s best not to use one if you can avoid it. Keeping the same connection eliminates potential leak points and can simplify future maintenance.
These are just a few of the items that are central to your air compressor pressure switch. Unless an upgrade has been made available, your best bet is always to match your new Switch to the older Switch as closely as possible.
Replacing the switch is straightforward on most compressors. This is a general process and your steps may vary, but it is standard for air compressor pressure switch repair:
Unplug the compressor so you don’t run the risk of shocking yourself or getting a nasty blast of compressed air. Open the drain valve at the bottom of your tank to depressurize it. Locate the relief valve and remove the line—usually ¼ inch—that goes to it. Remove the quick connect fitting, pressure regulator and upper pressure gauge from the pressure switch. You will need to use either a small pipe wrench or slip-joint pliers to remove these. Begin by loosening the nut securing the relief valve air line and pulling it up and out of its bracket. Disconnect the ground, neutral, and thermistor wires from your pressure switch. Grab the strain relief eyelet with your pliers or pry it up with your wrench to pull the cable out. Pull up and remove the old switch. Apply thread lubricant or pipe lubricant to pipe threads and piping components. Install the replacement switch by rotating it. Tighten the switch with your wrench. You may need to use a pair of pliers to hold the lower stub pipe against the tank for stability. Reassemble your plumbing parts and valves.
These are the basic steps to replacing your pressure switch and relief valve. More advanced compressors may have larger systems that are more complex and require a broader set of tools and parts to successfully replace your air compressor pressure switch and other parts.
When to call a professional
Sometimes a pressure switch will leak air when there is another problem in your system. A common cause lies in the relief valve itself. If your relief valve is leaking, you should see a professional for a full inspection and repair.
To determine if your problem is coming from the relief valve, we look for a leak when the air compressor is off. This type of leak means you have a problem with both the valve and the compressor tank check valve. Problems can include failure to close the valve, improper sealing, or even damage and cracks to any of these parts.
In this case, and with leaks due to wear and tear over time, it can be difficult to get the parts you need for your air compressor pressure switch. Contact our professional staff for a quick check if you’re having trouble getting parts or aren’t sure which parts you need.
Let’s say you tried to fix it yourself and you still have the problem of air compressor pressure switch leaking. Don’t just assume that your new pressure switch is defective. The tank check valve, relief valve and other elements may be responsible for your problems.
Turn to Quincy Compressor for your air compressor and pressure switch repairs so you can get the job done on time and on budget.
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