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2 stage valve simplify

2 stage valve simplify

2 stage valve simplify

(OP)
Greetings!
So today's random task involves one part reverse engineering, and one part experimentation.   Basically, the alpha proto of this product was derived from a standard hose pressure (80-120psi) retail watering timer.   The timing mechanism and design is irrelevant to our concern, but the two stage valve design is a useful option for our product.

As such, I have copied much of the mechanism and have a working prototype in SLS material.  It actually works better than I expected considering its our first try at this.  There are some features of the original that I don't understand the purpose of, however, most notably the two different sized pinholes in the rubber diaphragm component.  One is about .03" diameter and the other is probably .055" They are located at opposite apexes of the diaphragm profile and they would allow full line pressure to access the diaphragm on the top side as well as the underside.

The valve stem in this case protrudes through the low side pressure area and is sealed in a concentric plastic hub within the diaphragm as shown in the attached illustration. (Note that when the stem is acted upon, fluid is allowed through the narrow clearance between the stem & insert).

Now that I have a reliable working demo of this arrangement, I am working toward applying these same principals to a valve design which is flattened to a minimal vertical profile.  I'd like to squash the whole assembly to a pancake style profile.  I am approaching this task in a number of different ways, but I would like a better understanding of the pinholes and the reason for their varying diameter(s).  I would also like a better understanding of the importance of the low side pressure.  In our particular application, we really don't require a neat, precision contained flow at the end of the system as the original valve delivered.  

It would be fine to spray out randomly immediately past the rubber stopper or "cork" type feature.  I believe that we will still require a closed volume to create some back pressure, however.  

In any case, this explanation will hopefully be much clearer within the attached drawing.  

One variation has similar dynamics applied to a flapper valve design instead of a diaphragm. I wonder if the diaphragm's primary purpose in this case is to simply act as a seal & a spring for the insert.

Thanks in advance for any suggestions and/or explanations on the attached valve design.
-k

 

RE: 2 stage valve simplify

You have a "pilot operated valve". The valve stem with the o-ring seal is the pilot valve. It has a small area exposed to full water pressure so it takes little force to open it. When the pilot valve opens, it releases the pressure above the diaphragm, allowing it to be pushed-open by the fluid inlet pressure. When the pilot valve is allowed to close, then inlet pressure is applied to the top of the diaphragm through the small holes in the diaphragm, causing the valve to close against the inlet pressure. The difference in size of the orifices is probably just manufacturing variation. The orifices mast simply be "small" compared to the pilot valve area.

This design can be considered a hydraulic servo mechanism that uses energy from the inlet fluid to help operate the valve. It is a very common design in solenoid valves such as those made by ASCO. You can find more info on the ASCO website, I'm sure.

RE: 2 stage valve simplify

(OP)
Thanks Compositepro!
I'd forgotten the term pilot valve until you mentioned it- thanks!  The orifices appear to be intentionally different sizes across several examples we have examined.  I thought this might be a way to induce some turbulence that helped the sealing and unsealing of the main passageway.  That's the best theory I could come up with anyway.
In regards to the particular attachment in my post, do you think that we could eliminate the front section of valve? (low side pressure) Photo #2 partially illustrates what I'm proposing.  I understand that the resulting flow would be spraying out at random, but for this application that would be fine.

Also, do you think the rubber diaphragm shown could be effectively replaced with a (semi-rigid) flapper valve?

Thanks again for any info!
-k

RE: 2 stage valve simplify

(OP)
I'm going to reply to this for reference since I just tested out a few theories I'd described earlier:

Test #1:  I removed the spring, and replaced the rubber diaphragm with a simple flat rubber washer of the same inner diameter.  Where the outer diaphragm lip operated as a sealing ring, I simply replaced it with a separate O-ring set into the groove so that I could do this test.

Result: Most observable performance is about the same.  I was expecting a more delicate balance of pressure and flow for reliable operation, but I was pleased to see that overall my pilot valve was working with a simplified seal.

Test #2: I removed the pressed in guide washer (white) and the O-ring underneath.  I then cored out the front side around the exit flow port so that fluid flow is unconstrained (similar to illustration #2).

Result: Again, the valve is working as we had hoped.  I was expecting back pressure to play a larger role in its operation, but flow and effectiveness are nearly identical with the exception of some sealing alignment due to the absence of the guide washer/ring.

Thanks for the help, I hope someone else can also benefit from this information.
-k

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