Is this some sort of shut off valve?

[Tex N Oz]

This is some sort of secondary regulator that is coming off the bottom of a CO2 regulator.
I've taken it apart and can see that it's designed to shut down flow once the beer line pressure goes high. Is this to prevent over-carbonation?

It's off an Allbar regulator.

 

[dblunn]

It is designed to protect the keg form over-pressure in the event of a regulator failure. Cornie kegs have PRV but standard 50 L kegs don't.

 

[Tex N Oz]

It is designed to protect the keg form over-pressure in the event of a regulator failure. Cornie kegs have PRV but standard 50 L kegs don't.

But it's not a pop-off valve and there's no place for it to relieve. It only shuts down between the regulator and the keg.
I'm wondering if it's not some sort of second stage pressure regulator. That's what it's built like but I don't understand why it would need one.
It would however shut down the pressure if the main regulator diaphragm AND the cap vent hole got plugged but that's unlikely. Plus the regulator already has a PRV on the low side.

 

[MHB]

They are an SRV, Service Relief Valve, many incorporate a PLV (pressure limiting valve) but in the event of a major reg failure they will dump all the gas in the bottle, rather than blow up the keg.

Not something you see all that many of these days, most regs have built in fail save venting and 400kPa limits, and kegs are being made with burst zones that allow the keg to vent safely rather than explosively.

As above most home brewing kegs have a PRV, in my experience they are worth about $1.25 in scrap.
Mark

 

[Tex N Oz]

They are an SRV, Service Relief Valve, many incorporate a PLV (pressure limiting valve) but in the event of a major reg failure they will dump all the gas in the bottle, rather than blow up the keg.

Not something you see all that many of these days, most regs have built in fail save venting and 400kPa limits, and kegs are being made with burst zones that allow the keg to vent safely rather than explosively.

As above most home brewing kegs have a PRV, in my experience they are worth about $1.25 in scrap.
Mark

I've never seen a PRV or SRV that didn't dump the gas into the atmosphere. This just shuts off the gas between the line and the regulator but there is nowhere to dump the gas.

 

[Tex N Oz]

Ok I think I get it now. This is a pressure limiting valve. It's stamped on the side 475 which is the pressure limit of most modern kegs.
If the diaphragm of the regulator should fail and it starts to blow down more gas than the PRV can handle, it will automatically shut off the gas flow once it hits 475 in the service line.
That's not a bad idea to be honest. It sure beats having a rupture disc in the keg give way and filling your keginator with foam and ruining a good keg.
If like me you put your regulators in the fridge, it's likely to eventually happen at some point.

 

[Rocker1986]

I'm guessing he meant dump all the gas in the bottle into the atmosphere. You can't really dump the gas from the bottle back into itself.

 

[Helles]

Could it shut off gas supply to keg if there is too much gas flowing ie a leak
Similar to car LPG tank


edit Just beaten

 

[MHB]

I've never seen a PRV or SRV that didn't dump the gas into the atmosphere. This just shuts off the gas between the line and the regulator but there is nowhere to dump the gas.

 

[osprey brewday]

Seeing lots of these lately laying around in plant-rooms at a few clubs i do work at they must be all upgrading there old equipment.

 

[Tex N Oz]

Capture.JPG

That hole is the blow off port for a diaphragm failure. That screw cap (part with hole in it) holds a very thick diaphragm (red disc in picture) that actuates a piston. If gas ever came out that hole from an over-pressure that would mean it was enough to blow that very heavy diaphram. It's exactly like the hole that on the regulator cap in case of diaphragm failure.

 

[MHB]

Yes I am quite familiar with them, having pulled dozens apart.
The one you have there is an old model, probably over 25 years, for a device that was installed as a safety feature they were supposed to be serviced regularly, they rarely were, often leak, or get very sticky and surge so your set pressure goes all over the place.

Although they are designed to limit the pressure to around 450 kPa, the regulator is usually limited to about 400 kPa, the SRV is exactly that a Service Relief Valve if the pressure in the "low pressure" side of the service goes over 450(ish) kPa the SRV vents the pressure, if the over pressure is caused by a failure in the regulator, it will vent the entire contents of the bottle, through the hole, as you point out there is one on the reg to, it is there for the same reason, to vent if the reg fails.

Honestly they are more trouble than they are worth, especially if you have PRV's on your kegs.
Mark