mechanical replacement for solenoid valves and electronic timing

[y0da900]

Not that anybody seems to be doing much in here anymore....

Here is a pulse valve design I came up with not too long ago. I've had the concept in one form or another drawn up for about 2 years now, this is the first one that was actually drawn to scale and designed to be built and not just theoretical.

A 10-32 FCV with integrated check goes into the bushing/plug. A splitter fitting splits the flow to each end of the pulse valve, with the splitter fed from a normally closed 3-way valve. The air will fill the void without the FCV much faster than the FCV side, forcing the spool to shuttle to one side. As the FCV side fills (more slowly), the bias in area shifts the spool back the other direction (once a pressure/force balance is achieved), venting the initial side and providing air to the second output. Because the two sides are connected through the splitter, the spool is allowed to shuttle back and forth without compressing one side. The integrated check in the FCV allows rapid venting of that side without the same restriction present in filling the chamber.

Dwell is created by varying flow through the FCV (flow control valve, I should probably mention that). As the restriction increases, the time taken to pressurize that side of the spool increases, lengthening the dwell. Same for the opposite direction - reduce the restriction to lower dwell.

As long as the trigger pull is longer than your desired dwell time, this should work. You can plug outputs to create either a normally open or normally closed 3-way valve in addition to a 5-way valve.

I haven't built one yet, so this is still somewhat theoretical. But what little input I've gotten from others on it is that it should work.


Body/housing


Piston (updated 10-11-2008)


Bushing/plug

[Swiss Cheeze]

reduce those pics sizes so it's pleasant to look at.

[Hilltop Customs]

me likes...just to make sure I'm following this right, the smaller diameter side is instantly hit with high pressure while the larger diameter side has a limited flow rate. High pressure hitting the small diameter side moves it to the right as the large diameter slowly (not really slowly, but you get my point) fills past the force equalization pressure and moves the piston back to the left. When the trigger is released, air is released from both sides...but the piston will not move because the force differential remains as the air is released so the piston will remain to the left as both sides empty.

Sorry if thats wrong, I didnt get a chance to look at the pics much....I want to throw them in photoshop, make the piston one transparent, and play around with it. Probably just end up modeling it.

Only problem I can think of ATM is if a long dwell is required, high restriction will be needed. If the venting air also has to be processed by the FCV(if a normal 3 way was being used to actuate) there may be a problem with the large diameter side staying pressurized too long after trigger release....meaning you pull the trigger, but there is still pressure in the large diameter side so the piston doesnt move. A simple solution is to add a QEV between the FCV and the large diameter side of the body to speed venting.

I wonder what kind of accuracy and repeatability of dwell this little guy would create....essentially you could use this thing to make any electronic marker completely mechanical, even ones which require precise dwell control. That is sick!

[y0da900]

Yup, you've pretty much nailed it on the head. It might want a tiny spring on the large diameter side just to keep it in position at rest.

The integrated check takes care of your issue with venting through the FCV, it vents as if there were no restriction present. A QEV on each end might not be a terrible idea though, in addition to the FCV.

Can you view AutoCAD drawings? I'll send it to you if you can open them, it's AutoCAD 2007 format, but I can downgrade that easily enough.

I've got a variable volume expansion chamber drawn in the file that will take care of abnormally long dwell times, add that between the FCV and the pulse valve, and you automatically now need to pressurize that much more volume. Shouldn't be necessary in most cases though, I think a nice FCV should give nicely adjustable resolution.

[Hilltop Customs]

I should be able to open them, I have access to solidworks and pro-E, so I'm thinking one should be able to open it.

I dont think you would need a qev on the small diameter side, as the volume required to dump is low and the path to the vent should be direct with little restrictions.

ahh I had more to say, but I'm going to be late for my hair cut, I'll pm you my email when I get back.

[y0da900]

I already have it from sending you the slug file. It will be on its way shortly.

[Hilltop Customs]

Thanks for the file, I havent had much free time the past few days, plus I'm getting sick again(just had a cold a week ago) Hopefully get a chance to play with it later this week, probably not till friday....might use it for practice for master cam. If I do and if you want it, I'll send you the NC code for it.

PS: I'm so surprised there hasnt been more people noticing/responding to this, its so simple and its an elegant solution to the dwell issue. I may just sneek in making a couple of these if I can somehow make the time. Id just need to come up with a way to test the dwell output?!?! (never really thought about it be4, what would you use for something like that other than some type of computerized instantaneous pressure readout that records duration?)

[Hilltop Customs]

I think your right about the spring on the large diameter side in case of partial pull....if the piston is in mid motion or fully moved to the large diameter side and the gas is released before the large diameter side has fully pressurize, the piston may get stuck in the open position. It could be easily reset with one trigger pull, but I think, as you stated a spring with just enough force to reset the piston would work best.

edit: ps, what about a carburetor type needle valve to regulate the flow? should allow for fine adjustments...dunno if they would be fine enough though.

[y0da900]

Most FCV's that I'm familiar with are needle valves.

I think the response to it here, of lack there of, is two-fold. It doesn't readily relate to mags in any way. And very few people notice this sub forum, and fewer care or understand it.

[Hilltop Customs]

Had a few minutes between classes...so I modeled the piston in solidworks.

The file you sent opened up, but it was doing some weird stuff so I thought I'd build one off your dimensioned drawings. Probably model the rest after tomorrow between classes. I wish I had access to pressure/mechanical simulation software....might have to ask around different departments to see if I can come up with something. I'd really like to know how accurate this little thing could be.

looks sweet....wouldnt be too hard to make in quantities either.

[y0da900]

Something I plan on changing when I finally getting around to making one. The really thin dividing pieces should taper towards each other (on the wider portion, the narrower section is for an o-ring) for both strength and easy to make with an individual tool instead of facing down each side.

EDIT- Updated piston print above to reflect this.

[Hilltop Customs]

well heres an idea....I'm willing to bet you have already thought of y0da. I dont have time to work on ATM.....

take an SLG....replace the noid and valve with this little baby and a 3 way. Have everything run at the operating pressure of the dump chamber. Use the air coming from this valve to operate the sear release(similar to a pneumag).

only problem I see is adjusting the reg pressure could effect the dwell....but dwell doesnt really matter as long as the dwell resets the sear before the dump chamber repressurizes and sends the bolt forward again. Velocity wouldnt be dependent on dwell.....simply dependent on input pressure. You wouldnt need an adjustable flow control valve, simply a restricted orifice and flow distance to set the output dwell to an acceptable level.(an acceptable level through the range of pressures required for adjustment of velocity)






hope that makes sense