Fast opening valve

[sim1254]

Hello everybody

Does anyone know what kind of air valve fits the following requirements and where it can be obtained?

-It should usually be closed
-It should open within less than 10ms and stay open as long as it is activated
-It should withstand air pressures up to 500psi
-Its smallest inside diameter should not be smaller than 0.2 inches
-If possible, it should operate mechanically (no solenoids)

Any hints would be greatly appriciated. Thanks.

 

[Eyadbdc]

Please try this company maybe you will find your request

http://www.caleffi.com

 

[jsummerfield]

-It should usually be closed
Selection of the actuator permits failing the valve open or closed. Your description sounds like you want it to normally be closed and fail open upon loss of signal.

-It should open within less than 10ms and stay open as long as it is activated
This is very fast and most achievable on very small valves.

-It should withstand air pressures up to 500psi
The valve body and pressure containing components are easily obtained suitable for 500 psi. A pneumatic actuator signal would be unusual.

-Its smallest inside diameter should not be smaller than 0.2 inches
This is quite small and might be specified to prevent plugging. What is the capacity that must be released and over what time? You need to determine the body size. A quarter-inch ball valve from Whitey (Swagelok) is looking like your solution.

-If possible, it should operate mechanically (no solenoids)
I selected a pneumatic actuator based upon you mechanical description. Clarify if you mean a lever, or some other mechanism.

John

 

[sim1254]

Thank you for your help. It seems like I need to give a little more details.

Air is stored in a reservoir at a pressure of 500 psi. When the valve is activated, the air should be released immediately. The capacity that must be released is about 0.3 cubic inches over not more than 50ms. However, it should open as quickly as possible so that the pressure increase is instantaneous (well, almost).

The valve should be actuated manually, via a button, lever or something of that kind. It mustn't be electrical because there is no power supply.

I understand that the requirements might be difficult to fulfill and I have also considered making a custom valve but I first wanted to know if there are any designs around which fit my requirements. Thanks again.

 

[zdas04]

If you can live with local operation why not just use a manually-operated ball valve? Slam open a 2-inch ball valve and you should dump 0.3 in^3 within your 50 mS target (I haven't done the calcs).

David

 

[sim1254]

What do you mean by slamming it open? This is certainly not very precise, let alone fast enough. A ball valve requires some force in order to be opened which cannot be supplied within such a short time as 50ms. After the 0.3 cubic inches of air are released, the valve should be closed immediately to save air.

 

[sailoday28]

sim1254 (Mechanical) Dec 21, 2004
writes
Air is stored in a reservoir at a pressure of 500 psi. When the valve is activated, the air should be released immediately. The capacity that must be released is about 0.3 cubic inches over not more than 50ms. However, it should open as quickly as possible so that the pressure increase is instantaneous


What pressure is instantaneous? The reservoir? If so, what pressure does it rise from (initial conditions)
I believe you are indicating that this is a transient problem.

 

[israelkk]

When you say 0.3 cubic inch you should state at what temperature and pressure the amount released will fill 0.3 cubic inch. It is more accurate to give the mass of the air released.

Can you give the resevoir volume too? Because the pressure in the resevoir is dropping during the discharge process therefore the air flow rate is not constand during the discharge.

How accurate you want the 0.3 cubic inch to be?

Air will be discharge during the valve opening process (the 10msec) too i.e. from the command to open until it is fully opened and then during the closing process (10 msec?) too.

The valve orifice should be very precise and specific if the 0.3 cubic inch required to be accurate?

Can you use the pressure in the reservoir to activate the valve?

 

[sim1254]

The pressure increase in the tube after the valve is opened should be as instantaneous as possible. The reservoir is precharged. Apologies for not being precise enough.

The 0.3 cubic inch needn't be accurate, it is an approximate volume. The air inside the reservoir is at room temperature. Let's say the narrowest cross section inside the valve must be as big as possible in order to maximize flow rate, but not exceed 1/4" in diameter. The most important thing is that the time it takes from the command to the full opening is as short as possible.

>>Air will be discharge during the valve opening process (the 10msec) too i.e. from the command to open until it is fully opened and then during the closing process (10 msec?) too.

Yes, and that's precisely why I want the opening and closure time to be as short as possible.

 

[sim1254]

I haven't adressed these two question yet:

>>Can you use the pressure in the reservoir to activate the valve?

Preferably not because the reservoir is not very large (approx. 150 cubic inches) and air should not be wasted in the process.

>>Can you give the resevoir volume too? Because the pressure in the resevoir is dropping during the discharge process therefore the air flow rate is not constand during the discharge.

Since the flow is restricted by other things that come after the valve in question, flow rate is not important, hence pressure drop is not a problem.

I hope that helps.

 

[sailoday28]

Clearly you have in addition to valve sizing a transient analysis. In addition to questions by others, Temp, etc. What mass does the 0.3 cubic inch correspond to?
Is there piping downsteam of the quick opening valve?

 

[sim1254]

I think you are asking for information that I don't know. There is piping downstream of the valve, and there is a piston that blocks the pipe and moves when air is released from the tank. These things do not affect the choice of the valve.

The only important things are those that I mentioned in the original post:

The valve should stay closed unless the button is pushed so that air is stored in the reservoir. When the valve is actuated, air should flow out of the reservoir. The flow rate should reach its maximum as quickly as possible, hence the valve needs to open very fast. It should close as soon as the button is no longer being pushed. It should withstand pressures up to 500 psi because the air inside the reservoir is at that pressure and there mustn't be any leakage. It's narrowest spot shouldn't be smaller than 0.2 inches in diameter.

 

[monkeydog]

sim1254,
Do I understand that you want this "valve" to be no smaller then .2 inches diameter,
"It's narrowest spot shouldn't be smaller than 0.2 inches in diameter"

and no larger then .25 inches diameter?
"The 0.3 cubic inch needn't be accurate, it is an approximate volume. The air inside the reservoir is at room temperature. Let's say the narrowest cross section inside the valve must be as big as possible in order to maximize flow rate, but not exceed 1/4" in diameter. "

Is that external or internal?

Can you make a valve to look something like a gun (revolver) with the rotating chambers sized for the .3 cubic inches? You can recharge one chamber when discharging another.

 

[sim1254]

>>Can you make a valve to look something like a gun (revolver) with the rotating chambers sized for the .3 cubic inches? You can recharge one chamber when discharging another.

Well, I've got a number wrong, it should be 3 cubic inches instead of .3. But still, the idea with the rotating chamber can not be done because the reservoir has a volume which is given, as I've stated in another post (150 cubic inches).

>>Is that external or internal?

The dimension requirements for the valve are internal. I'll put this in other words: The smallest cross sectional area of the tube within the valve should not be smaller than say 0.035 square inches (this corresponds to 0.2 diameter). However, it shouldn't exceed 0.25" in diameter because the reservoir outlet is 0.25" inside diameter, so flow rate is already optimal when the valve has that diameter as well.

I'm looking for the type of valve that can do the job. What kind of walve is usually used when fast opening and closure are required?

 

[MikeHalloran]

That's not a fast valve, that's a damn fast valve. Most electric valves can't reach full current, much less move at all, much less move their full stroke, in 10 ms.

I've persuaded size 23 stepping motors to move itty bitty plug valves (1/16" aperture) by 1/4 turn in 50 ms. The motion looked instantaneous, but of course it really wasn't.

You need a basic valve mechanism that 'produces' a relatively large open area in a small amount of time, which would ordinarily imply a poppet valve. But you also need a substantial stroke to meet your minimum particle size spec, so the moving parts have to be relatively massive.

That, in turn, means that you have to apply a substantial force to the moving parts to accelerate them rapidly, and that implies exhausting some of that 500psi air in a pilot- operated valve, or using some other stored energy source. Simplest thing that comes to mind is a poppet valve that's opened by a sturdy button that the operator depresses ... with a hammer.

You might take a look at the valves that are used in paintball guns.






Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[sim1254]

Well, knowing very little about valves, I didn't expect it to be so difficult. Since most reflex cameras achieve exposure times of 1 ms, I thought that there might be valves that can do the same.

I now thought about a design which consists of a hammer and a poppet with a reset spring. All this is contained in an angled 2/2 way valve body. The hammer is cocked beforehand and is held in this position by a pin. As soon as the pin is moved out of the way, the hammer strikes the rear of the poppet shaft. The poppet is accelerated and it opens towards the outlet. It is then set back by the spring. The opening time could be regulated by some screw which precompresses the spring, or simply by choosing a different spring.

My question is: Since the poppet is only held in the closed position by the spring, the pressure from the inlet will open it on its own, right? How can you prevent this from happening? Since the inlet static pressure is very high, it will amount to a large force. The spring mustn't be too stiff, though because this requires a bigger hammer. On the other hand, you could reduce the area on which the pressure acts by making the outlet smaller and decreasing flow rate. How is this problem usually solved?

 

[MikeHalloran]

The usual solution for that problem is a pilot- actuated valve, where the poppet is held closed by a piston in an opposing chamber. The chamber is filled with supply air by a bleed from the upstream supply. Actuating the valve requires only discharging the contents of that chamber to atmosphere. Since the chamber is small, that can be pretty quick.

See 'force balanced' valves. See also trigger mechanisms for guns.

I was actually thinking of a poppet valve installed the other way, so the spring and the supply pressure both act to hold it closed, and the impact of the hammer forces it open.

;---

I think the first trick in camera shutters is that it's not necessarily the same element that occludes the light path at the beginning and end of the exposure. The second trick is that you don't need a big opening to pass a lot of photons.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[israelkk]

I have calculated the the transient process of filling the 3 cubic inch from a 500 psi supply. The theoretical results are:

1. The time to reach 63% of the final pressure (315psi) is 18 msec.
2. The time to reach 90% of the final pressure (450psi) is 28 msec.
2. The time to reach 100% of the final pressure (500psi) is 38 msec.

The calculations are based on an inlet orifice of 1/4" diameter with an orifice constant of 0.9. For orifice constant of 0.8 it will be 21 msec, 32 msec and 43 msec respectively.

I suspect that you may need even a faster valve than the 10 msec.

 

[sterl]

I know of no valve design except certain styles of safety valves that can react at these speeds. All involve energy storage...

Consider, though, an IC engine, with high spring rates on the exhaust valve return spring. Your 20 ms corresponds with the cam-and-spring arrangement operating at 3000 cycles per minute, which for a 4-stroke engine at 240 degrees or so of cam duration, seems to be 9000 RPM. Current motorcycle engines consider that mid-range....and 3 cubic inches is about 50 cc, and they would pass considerably more than that, and instantaneous pressures are at least of the same magnitude. Of course, the mechanism never starts from dead-stopped and is not dominant in the rotational acceleration equation...

COURSE, thats a 30 mm Diameter poppet, at about 5 mm of stroke.

If all that sounds like it could suit your need: the body still looks a lot like a high pressure SRV, but the mechanism to "fire" it still has some fun left in it...Something like a high torque spiral wound spring and a quick release sprag or brake might get there, but its a single shot weapon...And if thats what you need, so's a 12-ga.

 

[JSAkins]

I just saw your thread, if non-reclosing is okay check out

http://www.rupturepin.com