Pressure Maintaining Valve

[tbone1004]

@iain/hsm what BPR is on your compressor?

 

[Miyaru]

I don't know what the technical advantage is for a metal-metal seal.
Valve seat: teflon
1st stage seat: non-metal
(No idea what the used material is).

The one-way valve I have, turned out to be for hydraulic applications, not pneumatic. Since I couldn't get my hands on a valve suitable for more than 8bar, I tried a teflon ring (from a tank valve):

Without the teflon ring, the valve leaked air. With the teflon ring, it seals 100%. Compressor pressure is max 225bar, PMV is set to 140bar, both pressures tested just fine.

So if this works, the same idea might work for the PMV. Since I didn't have a suitable teflon ring, I took a valve-knob ring, drilled a 3mm perfect hole and cut the outer part to fit between both parts:

Teflon ring. Right size but way too thick.

The ring I used to cut a tiny custom ring.

Using this modification, I pressurized the PMV. Above 200bar, it's fully open. Below, it gradually closes the airflow and seals completely at 135bar.

This is the result after leaving the setup untouched during 2 days.

 

[Agro]

That's Coltri style, as cheap as possible. But other PMVs are not better, most of them "seal" metal to metal. For a compressor it is OK because you must maintain the pressure during work only. If compressor is not working no air passes the filter, no air has to be cleaned. As soon as compressor is running, PMV starts working and will maintain 140 bar, you do not realise any leaking.

But anyway a leaking PMV is nothing we like to have. And a PMV also has the function of a oneway valve, preventing oxygen going from cylinder into filter housing (boombang) in case you open the cylinder's valve to early (higher pressure in cylinder then in filter housing). In this case zero leaking is needed.

Therefor I decided to produce my own PMV by parts you find in a Poseidon Xstream first stage. Rubis ball, Zytel seat, O ring. What shall I say, zero % leaking. It's been working for many years without problems.

 

[iain/hsm]

@iain/hsm what BPR is on your compressor?

Er we are on the other side of the planet my friend. We only build quality products for professional divers over here. We dont do this scoobee doo junk
But if you need to know its the Hale Hamilton DR4 Mk 4 for the military
and for the little (SA-6ish) varient it's the Swagelok KBH model Build spec 1V0D4C6P60000.

For a sports diver I would go for the AquaEnvironment nickel plated brass version the model 211-B with viton rings.
With a 0.05 scfm leak rate but remember we use 200/300 bar DIN connections over here and the connection has its own closure valve pressure gauge and non return valve at the point of filling

 

[iain/hsm]

I don't know what the technical advantage is for a metal-metal seal.
.

You will after you run the thing for a while.

The gas moving across the BRP seat when opening moves at sonic velocity.
Any grit dust dirt activated carbon dust moly sieve dust etc and the gas density itself "peppers" the soft seat material. Akin to grit blasting. (even worse when compressing pure nitrogen)

As the HP seat begins to lift when the back pressure spring begins to lift the exiting gas rips anything soft very quickly (commercially speaking for say a dive shop application)

For a static pressure Nylon POM PTFE, Teflon Peek or any other soft seat material of choice will last for decades, For a dynamic pressure drop, or high velocity in a BPR application that soft seat will, leak and leak and leak.

Hence why you always see metal to metal seat designs in comercially available BPR designs. Although rising plug seals are an alternative, as is the rising taper stem designs that prolong the soft polymer material life. A 2um particulate in line filter also would help upstream of the BPR
But it will need to be a sintered bronze long tapered cone type not the oriface micro hole variety pack type. Having said that with the average sports diver doing 40 to 60 fills a year peddle to the metal on his Italian stallion lightweight compressor he wouldnt know much of a difference.

 

[tbone1004]

Er we are on the other side of the planet my friend. We only build quality products for professional divers over here. We dont do this scoobee doo junk
But if you need to know its the Hale Hamilton DR4 Mk 4 for the military
and for the little (SA-6ish) varient it's the Swagelok KBH model Build spec 1V0D4C6P60000.

For a sports diver I would go for the AquaEnvironment nickel plated brass version the model 211-B with viton rings.
With a 0.05 scfm leak rate but remenber we use 200/300 bar DIN connections over here and the connection has its own closure valve pressure gauge and non return valve at the point of filling

bit condescending lead in, but good to know. Was looking at new ones for mine, so will go with the Swagelok one, but probably the W version that's rated for 6000psi instead of 3600

On the metal to metal, you actually see that with the Poseidon first stages. The hard seat bullet will get scored over time from the air going across it which is fixable, but irritating. No way I'd want to use a soft material in there. If SS scores, the soft goods don't stand a chance.

 

[iain/hsm]

bit condescending lead in, but good to know. Was looking at new ones for mine, so will go with the Swagelok one, but probably the W version that's rated for 6000psi instead of 3600

On the metal to metal, you actually see that with the Poseidon first stages. The hard seat bullet will get scored over time from the air going across it which is fixable, but irritating. No way I'd want to use a soft material in there. If SS scores, the soft goods don't stand a chance.

Hahah For the lead in I dont know, it sounded perfectly OK to me. Do you think it was a little too honest for our more sensitive readers. It's for one of those times when you tell them if you dont like this your gonna hate what's coming sort of post. Consider it just the build up. Only kidding lol.

I guess it was one of those "someone has to say it" sort of posts. And who better than us lot.

On the Swagelok option look again at your required BPR settings and the flow capacity curve I think you have a 6cfm oil free so your after an 1800 psi to 3600 pressure set range. The W6000psi may be too rough a hysterisis range I will have to look it up though.

For practical cost and simplicity for a sports diving application consider the Aqua Enviroment model 211-B BPR and just fit a line valve like a Sherwood model YVA 3010 at the filling connection point with a gauge.
Not the cheap ISI Tiawanese junk copy and not the expensive Swagelok KBH series

You only asked me what I used, I answered only that, maybe I should have explained why each different application.

Now here's the kicker You noticed the wear on the Poseidon first stage, and it flows at a human inhalation rate of what 30 BPM with a inhalation flow rate less than any Scuba compressor.

Further even if you only ever filled the same cylinder you breathed from the charging rate off the compressor filling it through the back pressure regulator is greather than your breathing rate through the Poseidon. The temperature off the compressor is greather than any sea water you would care to swim in with the Poseidon, Further the average service life of a typical shop compressor doing 500 hours a year running even with your 6 cfm would be 2500 fills a year. That's 7 fills a day for 365 days of the year greather than your Poseidon and you will still find folk 10 years later using the same Aqua Enviroment BPR. Try that with your Poseidon and see what you got. Grinding paste and a wooden stick over the HP cone seat no doubt.

 

[tbone1004]

@iain/hsm it was a bit cheeky, you have ot admit.

When I looked at the specs it says inlet pressure is rated at the pressure range quoted, so I'll be ordering a pair of W's at 6000psi. One right after the final stage to get it to seat, then the other after the filters.

For anyone curious, I just had a heart attack when I saw the Swagelok price. Just shy of $1200 for that BPR vs $200 from Aqua-environment