What kind of valve will do this? 1

[bdr16]

I am building a system which involves an increase in internal pressure via an air tank in order to extend a series of telescoping tubes, and a subsequent full release of pressure back to atmosphere. For safety reasons I need the release to happen due to the internal pressure reaching a certain point, and for the exaust valve to stay open until pressure has been fully equalized.

The system is carry-able and small, and operates at low pressures (<50 psi most likely).

Other than using rupture discs, is there a kind of valve that will do this?

 

[zdas04]

Any kind. Unless I misunderstood your requirement, it sounds like you want to manually introduce pressure, then manually release it. To save the pressure in your tank you might use a 3-way valve to either allow pressure or vent, but you could do it with 2 valves just as well.

Often, people get too clever with their problem description because they don't want us to steal their great ideas. If there is more to it than I've addressed, you'll have to give us more information.

David

 

[bdr16]

No, it's about like I said it is. My system ideally involves 1 electronic switch to introduce pressure into the system, and then once the pressure gets to a certain point all the pressure gets released. I read that a 3 way valve will only release pressure until the point at which it started to release, did I misunderstand?

 

[zdas04]

A 3-way valve is just an arrangement of ports. As long as the chamber is connected to the tank, pressure in the system will move toward tank pressure. As long as the chamber is connected to atmosphere it will continue to vent till all the gas is gone.

Look at

http://www.ascovalve.com/applications/Products/Solenoid3WayData.aspx

for a collection of 3-way solenoid valves. Read the paragraph at the top of the page.

David

 

[ash9144]

3 way valve is just a valve with 3 positions. What you do with these positions is your decision. So you could have position 1 allow air in from pressurized tank. Then position 2 open to atmosphere when a certain pressure is satisfied.

 

[bdr16]

hm, ok. So, if I wanted the arrangement shown in the attached picture what kind of 3 way valve would I want? I don't have any personal experience with fluid systems.

thanks!

 

[moltenmetal]

If the valve being used is a solenoid valve, "3 way" is a bit of a misnomer.

What it sounds like you need is what is commonly known as a a 3/2 way solenoid valve. This valve will have a P port (to which your source of pressurized air will be connected), an A port (which you connect to your device, and a vent. When energized, P will be connected to A and you'll pressurize your device. When de-energized, P will connect to vent. This is the standard valve used for single-acting actuators, which your device would seem to be.

3/2 way solenoid valves are cheap and plentiful, and are available in a wide range of sizes (Cv values, i.e. affecting how fast your actuator will pressurize and de-pressurize). They are available both pilot operated and direct acting- a pilot operated valve for your situation will be cheaper and will take less power.

 

[bdr16]

Moltenmetal, you rock. Thanks for making everything so clear.

I think I'm good then! thanks guys!

 

[hydtools]

A three-way valve has three ports. A 3/2 valve has three ports, two spool positions.

Ted

 

[moltenmetal]

Sorry- I meant to say that P will be dead-ended and A will connect to vent when the solenoid is de-energized! Wish this forum let you edit your posts!

A 3/2 way solenoid valve is distinguished from a true 3-way direct acting solenoid valve in that there always must be pressure at the P port for the thing to work, since the pressure at the P port is used to operate a pilot (such as to drive a spool back and forth as hydtools mentions- but there are other types of pilots- not all solenoid valves are spool design).

A true or "universal" 3 way solenoid valve can have the supply pressure at any port, and doesn't need pressure at any port to function. They usually have big coils and small Cvs and modest shut-off pressures.

 

[bdr16]

I have a concern, I need for the system to pressurize, then remain pressurized for a period of time, and then to vent the pressure and return to normal. It's sounding like a 3/2 way valve will pressurize and then immediately exhaust as soon as the signal to pressurize stops being sent. Have I misunderstood?

 

[jmw]

Pressure switch with high and low settings and a time delay off latching relay....?

JMW

http://www.ViscoAnalyser.com

 

[moltenmetal]

bdr16: yes, a 3/2 way valve will connect P to A while the solenoid is energized, and will connect A to vent as soon as the solenoid is de-energized.

You can actuate this with two separate signals using a latching relay, if you don't want to maintain the solenoid hold current throughout the period where the actuator is pressurized.

If what you really want is a valve to pressurize the actuator then block in the air (once a certain extension or pressure is reached), and a separate valve to vent the air from the actuator, then you need two separate 2/2 way solenoid valves.