Spunding Valve

[MrSheen]

Sure, this is the kind of PRV you would want on a reaction vessel or tank, to maintain very tight conditions upstream.

https://straval.com/products/relief...ol-inline-threaded-rvi-20/?size=16#size_table

That's a fun page to look at because you can get an idea how much how much certified process equipment costs, a little exy for the average homebrewer, but in principle a diaphragm is the direction i would head for a small blowdown pressure drop

 

[koshari]

Absolutely agree, I set mine to 15 PSI using a CO2 bottle. I put it on the fermenter on day 3 and have to check it twice a day. It will be perfect on 15 psi one time, the next time I look it will be on 5 psi, adjust the valve less than a tiny turn and next thing I know i'm at 30 psi, just touch the valve and it releases to 10 psi...

They work better in that range with a lighter spring.

 

[RobB]

Here's one valve manufacturer which makes them for as low as 0.5 psi (0.03 bar) : https://straval.com/products/relief...ure-diaphragm-control-inline-threaded-rvi-20/

From the same page: This is a diaphragm low-pressure valve which is used where accurate set pressures must be maintained. The large diaphragm area compared to a piston pressure relief valve produces much more accurate pressure control with very low hysteresis between opening and closing pressures. So I think there's merit in the idea and time will tell if the KegLand versions are as effective as the ones which I posted, which are probably made to a fairly high spec. I'll get one added to the box when the new 25L fermentasaurus comes in and take it for a test drive.

 

[wide eyed and legless]

They certainly look good but they could be pricey,when I was looking at diaphragm valves a while back the Parkers were over $200 but those above with the different spring options look the goods, the spring which fits the range 2 to 25 psi would be the choice,which makes sense as the higher the maximum the higher the minimum the KL one is a max of 40 psi so the lower end would have to higher also.
Have you sent an inquiry for the price?

 

[malt and barley blues]

The Keg Land ones start at zero.

 

[wide eyed and legless]

0 to 40 psi doesn't mean it works within that range, the lower end will be higher, just depends how much force is needed to make the spring start to compress, might come in somewhere around 5 to 7 psi.

 

[MrSheen]

The lower bound of its pressure relieving application will be determined by the springs stiffness and also depend on the length of the spring carrier compared to its uncompressed length, as well as the diaphragm properties and valve seat design.

It could be 0.5 psi, it could be 5 psi, I think some testing will give us this value.

The upper value (stated at 40 psi) depends on much of the same properties but is easier to roughly determine, it's the force of the spring at its shortest adjustable position (most compressed) * the area of the diaphragm acting on the spring pusher. but again it will be interesting to see through testing if that is an accurate upper bound.

 

[MrSheen]

sorry that * should be a /