So anyone built a Pressure Maintaining Valve / Priority Valve?
Need some hints on dimensions.
Need some hints on dimensions.
Anyone built a PMV?
- Thread starter Chickenthief
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A PMV is one of those things that can be useful but very few of us use them as they are really not needed for the way we use our compressors and filter media. The only reason they are in existence is to keep large amounts of moisture out of your desiccant. Because introducing large amounts of water in some types of desiccant can cause rapid expansion and destroy stuff. I have as yet never heard of anyone working with the compressors, we use for our PCP guns, have this problem.
Still to make your desiccant last the very longest it possibly can a PMV can be helpful.
Several here have built them so I would expect they will chime in.
Still to make your desiccant last the very longest it possibly can a PMV can be helpful.
Several here have built them so I would expect they will chime in.
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biohazardman,
If you are merely topping off tanks, then a moisture trap and desiccant might be sufficient. But if you are filling from low pressures, without a PMV, you might quickly saturate the desiccant.
Under high pressure, the water will condense out in the moisture trap. If you are pushing low pressure air through the system, water won't condense out, and the desiccant ends up taking on the full responsibility of moisture removal.
If you are merely topping off tanks, then a moisture trap and desiccant might be sufficient. But if you are filling from low pressures, without a PMV, you might quickly saturate the desiccant.
Under high pressure, the water will condense out in the moisture trap. If you are pushing low pressure air through the system, water won't condense out, and the desiccant ends up taking on the full responsibility of moisture removal.
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Thanks for that. Yup topping off our guns and tanks is what we usually do so that's why it has not been such a problem. I have run my desiccant filter for over a year now and it is showing some serious signs of moisture intrusion. So guess I will be replacing it very soon now.
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I'm getting a (proper) compressor so filling tanks (from zero) will be a thing in the future.
But they want over €210 for one so i will be building one from scratch.
But they want over €210 for one so i will be building one from scratch.
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I'm no expert and maybe I don't really understand the context , but I use a PMV on the output side of my filter it's a 1750 psi one as it stays closed until that pressure is met and is necessary for compressing the air before leaving the filter in order for the filter to do it's job of moisture removal. This happens when the compressor is building pressure, just passing air though the filter uncompressed does nothing to remove moisture.
It's nothing I built just purchased and installed. I let my compressor build air at or near my tank pressure before I open the tank valve.
If I have misunderstood your post sorry
It's nothing I built just purchased and installed. I let my compressor build air at or near my tank pressure before I open the tank valve.
If I have misunderstood your post sorry
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Also called a BPR (back pressure regulator). $68 in the USA
https://www.nuvair.com/1-4-fnpt-to-1-4-mnpt-6000-psi-back-pressure-regulator.html
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I bought the Alpha filter from Joe Brabcato right after getting my Yong Heng compressor years ago. The Alpha filter has a PMV set to 2200psi. I was thinking $400 is a lot of money for this thing but I'm very happy with it.
https://youtu.be/eBd9VF2OoxI?t=328
https://youtu.be/eBd9VF2OoxI?t=328
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Me being in Denmark this is the "deal": $68 + shipping $25? + Danish WAT (25%) $23.25 + Customs fee $26 = $142.25
For that kind of money i can spend an hour or two in the shed making my own.
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Because I use a hand pump I dont like the wasted pumps to pump up the cavity for the separator so I made something to keep some presure in the unit. Maybe I should have bought one but I just bought a valve on one end to keep the presure in the cavity and a quick connect fitting with a integrated one-way valve on the other end.
Allen
Allen
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I build MKI this afternoon and it went off like a fart in a diving helmet, well not totally but it can work and will be improved upon.
I started with a brass insert with a cone that enters the feed hole, spring tension was so high it marred and let go with a pop so loud i almost popped a nugget in my undies. Next i turned it down for a loose fit and tried an O-ring in a groove, that was the fart part, no good at all.
I found a suitable bellbearing that will be the donor of a ball suitable to block the hole. Then a new brass guide will be turned and hopefully that will be something to work with.
I started with a brass insert with a cone that enters the feed hole, spring tension was so high it marred and let go with a pop so loud i almost popped a nugget in my undies. Next i turned it down for a loose fit and tried an O-ring in a groove, that was the fart part, no good at all.
I found a suitable bellbearing that will be the donor of a ball suitable to block the hole. Then a new brass guide will be turned and hopefully that will be something to work with.
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Could I ask a question, that is open for discussion? A priority valve stays closed until the set pressure is met. What would happen if you keep your tank closed until the pressure you desire is met then open the tank valve. If the compressor SCFM was enough the pressure would be maintained. I have never tried this with a tank valve, just shooting from the hip.
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A PMV works like this:
A pressure of lets say 2000psi is set.
The compressor is started and works up to 2000psi.
Now the valve starts to leak but maintains 2000psi on the input side.
Until output side is above 2000psi the valve is restricting flow and keeping 2000psi on the input side.
This is only done for "true" diving compressors.
See they have a water seperator tower and that needs pressure of a min. of 2000psi to function properly.
A little math:
30% moisture at ambient airpressure means 300% when compressed 10 times (143psi), now top that to 2000psi (140 times ambient) and moisture content is 4200%. That is going to condensate and drip right out the bottom of the trap. If you still carry 100% then you have lost 30/(4200-100) 4100=0.007 ie some 99.3% moisture reduction and then you have a desiccant stack that will drive that number down further.
Thats why a PMV (pressure maintaining valve) / BPV (back pressure vlave) / PV (pressure valve) is important for water seperation in compressors!
A pressure of lets say 2000psi is set.
The compressor is started and works up to 2000psi.
Now the valve starts to leak but maintains 2000psi on the input side.
Until output side is above 2000psi the valve is restricting flow and keeping 2000psi on the input side.
This is only done for "true" diving compressors.
See they have a water seperator tower and that needs pressure of a min. of 2000psi to function properly.
A little math:
30% moisture at ambient airpressure means 300% when compressed 10 times (143psi), now top that to 2000psi (140 times ambient) and moisture content is 4200%. That is going to condensate and drip right out the bottom of the trap. If you still carry 100% then you have lost 30/(4200-100) 4100=0.007 ie some 99.3% moisture reduction and then you have a desiccant stack that will drive that number down further.
Thats why a PMV (pressure maintaining valve) / BPV (back pressure vlave) / PV (pressure valve) is important for water seperation in compressors!
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G
Guest
Guest
That is what I do. I top off my tank at 3500 P.S.I. and open the tank valve when the MCH-6 gets to 3500.P.S.I., but I am not filling from empty. If filling from empty it might work to let the pressure build in the compressor and slowly open the valve to maintain pressure.
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MKII is done and it works 100% 
I made a thingamajig with a 7mm steel ball that is pressed against the 3mm hole in the adjuster.
It has very slight blow by (maybe 1liter/min) and is rather precise to adjust and there is plenty blow by for 100liter/min.
A female Foster and some Loctite and i'm done.
Open for questions if anyone is interested!
I made a thingamajig with a 7mm steel ball that is pressed against the 3mm hole in the adjuster.
It has very slight blow by (maybe 1liter/min) and is rather precise to adjust and there is plenty blow by for 100liter/min.
A female Foster and some Loctite and i'm done.
Open for questions if anyone is interested!
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Thanks for sharing. I like design and machining if only to learn the person's thought process. Please share your other projects if they're airgun related.
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Here or in a new thread?
There are loads of home made tidbits i was to tight to buy and just made instead of watching the tube and get dumber.
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