by Shaun

mega suspension in the very early stage

mega suspension in the very early stage

Hi I am buidling a 4x4 suspension using a single air bag.I need this bag to operate at two heights.

At the lower height pressure would need to be 5psi and at the higher height the pressure would need to be at 30psi

what valve do I need to do this.P.S. the airbag has only 1 port.Thanks

Bill says...

If it were me building this system I would use a 5 ported valve, with two exhausts, three positions, with the center position to exhaust.

With the valve shifted to one end, that working port would flow 5 PSI to the air bag, with that ports normal exhaust port being used to supply the 5 PSI air.

When the valve was shifted to center, that would allow both ports to vent to exhaust and allow the bag to deflate.

When the valve was shifted to the other end, that would allow the 30 PSI air to flow to the bag, and it would maintain that pressure until the valve was shifted to center again to allow it to exhaust.

Go to this page - - for more info on 5/3 valves.



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Aug 04, 2010
4x4 with a difference
by: Anonymous

Thanks for the reply.I do have a 5/2 valve in my possesion and will try this first.

Might work. Make sure you plumb the two pressures in through the exhaust ports, and use the supply port as the common exhaust.


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Solinoid valves

by Karwan

why some times solinoids with two coils used on pneumatic systems?what is the difference with one coil ?

Bill says...

Hi Karwan. Nice to hear from you.

A single solenoid air valve usually has an internal spring to shut off the valve when the coil is de-energized.

If you have two coils, then the valve will require to separate electrical signals to shift the valve to both positions, and in some cases, the circuit designer will specify this specifically.

For example, a single solenoid valve, in the event the power is lost, will default to the position that the spring dictates. A double solenoid air valve will, in the event of a power loss, stay in it's last position.

Much more info about air valves is located on the valve pages of this website.



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May 07, 2011
solinoid valve
by: Anonymous

Dear Mr. Bill,
I do appreciate your prompt reply,your worthy information.


You are welcome.


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5/2 valve Advantage

by Prateep

What is the advantage of 5/2 valve over 4/2 valve in pneumatics.

Bill answers...

Hi Prateep. Thanks for visiting and writing in.

A five ported compressed air valve can have exhaust flow controls installed in the exhaust ports, enabling different extend and retract speeds on the actuator.

Or, if the valve spool allows it, you can plumb supply different supply pressures through the two exhaust ports, using the original supply port as a common exhaust, and have your actuator extend under one pressure and retract at another.



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Latching valves application

by John E.

I'm having problems finding a couple of valves. Honestly, it's because I don't know how to ask the Internet...

I have an application, an inert gas cooled furnace. Now, controlling gas flow via a gas flow valve is relatively straightforward. That is, I can use an off-the-shelf flow control that will measure and control gas flow. Works great during normal operation. Call this valve A.

However, I need a fail safe. Simplest seems to me to be a latching valve (Valve B) that turns on during the run -- powered on-- but requires negative power to turn off.

In this way, I'm protected in the event of a power failure, an all too common occurrence. If I place an "on-off" valve in line with my controller, I can set the controller to always allow a certain (tbd)scfm (ie, "off" is not controlled at "A" but at the "B"). Problem solved! As long as the valve B is open, I have some flow. Never mind the gas line -- this is tank gas, so power failures don't affect it.

And this is what I can't seem to identify well enough to find on the internet... What would I / should I be searching for to find Valve B?

Cheers, John

Bill answers...

Howdy John.

Hmmmm....I'm not entirely sure what it is that you seek.

When you say you need a "fail safe", what is the circumstance that needs to be so? And what is the condition of the "fail safe"?.

I have read and re-read your original message, and I'm not sure I get it.

Let me ask you this. If your Valve A powered up with an electrical signal, and the output from the valve also shifted an in-line air-piloted check valve, would that not suffice?

As long as there's flow from the valve A the check valve would remain open.

If the power failed to the electric solenoid valve A, then the outflow would cease, (assuming it's a spring return 3/2 style) and then the air pilot operated check valve would also close, shutting off the flow.

Is this close???

Cheers back at ya....


Comments for Latching valves application

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Sep 12, 2008
Latching valve / check valve
by: John


I think that's exactly correct.

Power to A allows flow.
oops, power fails. Darn power company.
Check valve keep flow going.
My process is incomplete, but safe!

Power comes back on, about 2 hours later.
everything has cooled, I manually reset furnace with power off signal to A.

Sounds like this setup with a check valve is a common thing? And I should be able to find such a thing readily.

Should I be looking for two separate items then, a solenoid valve and check valve, or is typically a single unit?

Thanks for your help!


Hi John:

You'll need two items. Your local industrial pneumatic supply house should stock both. When you call them make sure you know what voltage the solenoid uses, and what flow you'll need through the valve.

Again, I'm still confused about what it is you are trying to accomplish.

The air piloted check valve will only allow air to flow through itself when it's got an air signal to it. When the air signal to it stops, the check valve closes, and no air can flow again until the air pilot signal arrives again.

The solenoid valve will only flow air, if it's an NC (normally closed) valve, when there's an electrical signal to the solenoid. In the absence of the electrical signal the flow through the valve should stop.

Until I understand what it is you are trying to accomplish with your "fail safe" I'm afraid I can only provide a general response.

If you have an interest in me doing a circuit for you, send me an email with your contact information through the contact form on this site and I'll call you back with details.



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Is there any such thing as a 2 point latching check valve?

by Arkain
(Jonesboro, AR)

Here's the scenario...

Suppose you have a compressor tank and you want the pressure to be vented at a certain high pressure. Just about any kind of check valve will do this.... But suppose you want the vent to stay open until the pressure drops below a certain level. Is there any kind of automatic valve setup that can do this? Preferably without electronics?

Howdy Arkain...

The answer is yes, you can have a pneumatic-only circuit that will do the following:

1)When a high set point pressure is reached in a pressure tank a valve will open to vent the pressure and stay open until...

2)A low set point pressure is reached inside the same tank and then the exhausting valve will shut, and stay shut until the high pressure set point is reached again.

If that's your desire, either talk to your local fluid power supplier and ask them to create the circuit for you. They might do so in return for supplying all the components you will need - at least I used to do it that way :-) - or contact me via the contact form on this website, and I'll send you an estimate to create the circuit for you on paper.

You would then contact your fluid power supplier to purchase the components as per the bill of materials on the drawing.



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Using a 2/2 NC valve for compressed air storage

by Stuart Curtis
(Southampton, UK)

Simple diagram of usage

Simple diagram of usage

Hi, I know in the article it says that the 2/2 NC valves are not normally used for closed vessels but how about in the following situation?

We are designing a 'green' energy production method for developing countries and wish to store solar power generated electricity as compressed air. We were thinking of using a set-up as shown in the drawing attached, where the red squares represent the valves. As a bank of cylinders will be used and we would like to open the left valve, fill it to ~200bar, close that valve before starting to fill the next. Later when the energy is needed, open the right hand valve which goes to a turbine until the pressure has equalised.

As each cylinder will have a separate intake/takeoff would 2/2 NC valves be suitable?

Bill says...

Thanks for the diagram. It makes understanding your application easier.

If you have a 2/2 upstream from the cylinder, (to the left in the diagram), and the 2/2 valve in the downstream position (to right right) that is closed, as long as the air pressure in the upstream line is higher than the pressure in the cylinder, and the upstream valve is open, then air will flow into the cylinder, as opposed to flowing on downstream.

When the cylinder is full to the desired pressure, the upstream valve stays open, but now you open the downstream valve.

The compressed air will always flow from high to low pressure, trying to get back to atmosphere, so that the air in the first cylinder will start to flow to the low pressure point, and if that's downstream to the next cylinder, that is what will happen.

In order to keep the compressed air from flowing back upstream (if the air pressure there drops ) consider a check valve upstream of the cylinder, but to the right of the 1st 2/2 valve. Then air can flow into the cylinder past the check valve, but cannot flow back upstream if the air pressure there drops.

Adding a check valve downstream of each primary 2/2 valve will provide the benefit you seek.

You don't indicate what's operating the valves. Are they solenoid valves operating with electrical signals from a PLC?

It were me, I would also put a 2/2 valve in the drop line to the cylinder. I'd have it open as long as pressure in that cylinder was below optimum, then close after the cylinder was filled to a set pressure point to allow the supply pressure to then move downstream to fill the next cylinder.

The control loop would open those drop line cylinder valves in sequence, as the stored pressure / energy was needed to run the ultiamte downstream device (what, a generator?).

Most interesting application. Please keep us all updated.



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May 16, 2010
Thankyou and more info!
by: Stuart Curtis

Thanks for the answer, was very useful!

Yes upstream is a compressor and downstream of the bank of cylinders is an air generator (Tesla turbine).

Yes they will be solenoid controlled valves, opened and closed by a logic control system, depending on demand required.

I was considering putting the cylinders in "parallel" if you see what I mean so the valve on the drop line i dont think is necessary.

Would the check valves be necessary? If the left valve was closed so as not to let any air in so the compressor could be compressing the next cylinder, if the pressure dropped on the left, i.e the compressor was turned off, would the valve not stop the back flow?

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Air valves - Can you supply me with one?

by Patrick
(Lexington Park Md, USA)

Trying to find a trucker style valve with a 1/2 " or 5/8 NPT line. Do you carry this?

Bill says...

Hello Patrick. I get so many requests to supply parts and air compressors, maybe I should go into the business?

But no, I'm sorry, but the only thing I supply from my website is information.

Perhaps, if you go on the Valves page, some of my advertisers may help you?

When you say Trucker Style, do you mean DOT approved? If so, maybe Google DOT valves and see what pops up?



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Solenoid Valve questions.


Hi. I'm in China. As it is hard to explain to my workers some things I need, I decided to do some simple tasks by myself.

I've found so interesting this pneumatics field that I didn't enter before. I'm Mexican. Buying pneumatics stuff in Mexico is so expensive. Here, just 1 or 2 cents of USD for any piece you want, so the possibilities are infinite...but, for that price, I won't get enough support, so I look for assistance from you.

My questions are these....

Bill answers...


Francisco. Very nice to hear from Mexico via China!

I've taken your questions and listed them below, and answered each as best I can.

#1) What is the small bolt located at the bottom of the solenoid valves? This bolt may be pressed down and turned about 90 degrees.

Answer: Without seeing a photo it's hard to be sure, but I suspect what you are referring to is a manual over-ride. This allows the valve to be shifted manually during machine set up, and is particularly useful when the power is off.

A valve manual over-ride Is also a good way to diagnose a fault in a circuit. If an air cylinder isn't responding as it should, once you've made sure it's safe to do so, you can manually actuate the valve with the over-ride, and if the cylinder works while you are manually operating the valve, that would suggest that the fault in the circuit is in the valve, not the cylinder.

#2) What is the difference of a valve with a single or double solenoid? I mean the difference in functions.

Answer: Most single solenoid valves shift when the solenoid is energized. In the absence of an electrical signal to the solenoid, and internal spring inside the valve returns the spool to the de-energized location. That's a single solenoid, spring return valve.

If you have a double solenoid, then the circuit designer decided that he didn't want the valve to shift back when the solenoid was de-energized. Adding the second solenoid instead of an internal spring return would accomplish this.

#3) I've seen some applications that have a small tank (something like an accumulator). What is that for?

Answer: Again, very difficult to be sure without seeing it, but I suspect that it's a pneumatic timing device that will allow an air signal to decay slowly in an air control circuit, thereby allowing something else in the circuit to occur before the valve shifts back.

#4) There are some devices that feed (step by step) a coil of material into a press. In my factory we punch brass (to make key blanks) and we are considering to purchase one of these air feeders but would like to know how it works. Do you know them? Can you help me to understand?

Answer: There are a number of pneumatic companies that make pneumatic press feed circuits. Yes, I do know how they work. In terms of their function, it's a system whereby an air circuit alternately clamps, strokes, un-clamps and returns to feed a fixed length of product into a press.

I'm afraid if you're looking for installation assistance, you'll have to either get a local vendor to help, research press feed circuits from some of the pneumatic manufacturers around the world, or pay me to come to China to help! I was there a few years back, and wouldn't mind visiting again. :-)



Comments for Solenoid Valve questions.

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Jul 14, 2009
by: Francisco

thanks a lot for your replies. i send now the pictures of the bolt in the solenoid valves and the tank i mention to you. in this picture, the tank is in the air feeder that i also mentioned to you but also saw in other equipment as such as automatic welding machines and some clutches.

about your visit... let me consider it. crisis is hard so i can't promise...

some things, i'm interested on install and i assume that the suppliers will do good, some others, just want to know how pneumatic stuff work. i'm new on this.

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what are the advantages of 5/2 over4/2 pneumatic valve

by ajay munda

what are the advantages of 5/2 over 4/2 pneumatic valve

Bill says...

Already covered in detail on the pages to do with air valves on this site.

Start with the link from the nav bar VALVES and read the pages.



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by Peter
(Lansing Mi.)

I have a motorcycle lift that is air operated. The control valve has broken. I would like to replace it with a new one. What options are availible. It lets air in to raise and lets it out to lower. It is manually operated.
Thank you Peter Root

Bill says...

Hi Peter. You need a Normally Closed, manually operated, 3 ported, two position, air valve.

Have a look at the Valve pages for more info on what this means, if you aren't sure.

Or, take the valve off your motorcycle mount, and visit your local shop that sells air valves and air cylinders. They'll fix you up, I'm sure.

If you have NEFF Engineering outlet nearby, they'll fix you up with a MAC valve, at least, they used to rep them.



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Pneumatic Circuit Valves

by Abhijit

Respected Sir,

I am very much impressed to note that you have explained different types of valves very efficiently.I am very much thankful to you for that.

I am an Mechanica engineering student.

Could you please explain to me the electro pneumatic actuation of 2 air cylinders for the movement?

I will be very much thankful to you if u can assist me in giving me an explanation the way it's given for the 2/2,3/2,5/2 valves.

Your sincerely


Bill answers....


Thanks for visiting and for sending in your question.

I do regret that I'm not at all sure of what it is you are looking for? Perhaps you might write back and give me a bit more information about your application.



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What is the difference between spring return and differential return air valve?

by Muntaser

What is the difference between spring return and differential return and where I can use each one?

I use 5/2 valve with differential return to control cylinder but this valve is suddenly stopped so when I used another valve with spring return it worked.
Bill Answers...

Howdy Muntaser:

Whoever designed your air circuit has determined that the application is best served by using a 5/2 air valve that contains a differential air pressure return of the valve internal spool to shift the valve, and usually retract the piston rod of a double acting air cylinder.

Usually, a differential return valve will contain a spring as well.

The different force created by different surface-area sized pistons on the internal spool will use the valve supply air and the internal spring to shift the valve back when "something" has been accomplished in the air circuit.

It's hard to visualize why a differential return valve was used in the circuit without seeing the drawing or understanding the complete application.

A simple single-solenoid, 5/2 spring return is the most commonly used 5/2 valve, and the spring, when the single solenoid is de-engergized, will shift the internal valve spool back to the pre-energized state, allowing the piston rod on a double acting cylinder to retract after work has been performed.

I don't know know your circuit, but I expect that your circuit designer wanted a non-complex method to shift the valve spool back, and thus retract the air cylinder, without adding additional signal or control elements in your circuit.

When the differential valve is working, your cylinder will likely extend to do work, and after the pressure in the cylinder (and through the valve) has reached line pressure, the valve internal spool will shift back, and your cylinder will retract.

If you wish to use a simple 5/2 spring return valve, you'll need to add some control elements to the circuit to signal a valve shift when the work is performed.

Your present valve likely has a build up of contamination (see here for more info) which increases the friction between the spool and housing, and the air/spring differential can't overcome that friction to shift the valve.

Hope this helps.



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