how de regulators relive output presure

[iknowmy3tables]

I was designing a little sumthing involving a special regulating system and I now how regulators automatically close and open to regulate pressure but I don't know how regulators automatically relief the excess pressure from the output side when the regulator is adjusted to a lower presure

does any one know how that works most diagrams and sources don't say

[DYI]

My N₂ reg doesn't do that, and it's pretty high quality. What reg is it that you're thinking of that does this, and why?

[Ragnarok]

Hmm, I doubt such a thing would be used on a high pressure tank regulator.

Not all regulators will do such a thing, only relieving variants, which are a bit of a nuisance really, because I've been looking for regulators that don't do that, and they're fairly hard to come by cheaply. I could just bung a check valve downstream, but that's extra cost, components, more to go wrong, and more space in a design. Groan.

I imagine it's a bit like a safety pop-off, but a little more sophisticated.

[clide]

Well it would probably depend on the specific regulator, but one way it could be done would be allowing movement of the piston in the direction opposite of the way it moves to open and then have a hole to the atmosphere that is exposed when the piston moves a little in that direction. That's probably not very clear, but in most cases it is probably just a hole that the regulating mechanism moves past when the output pressure is higher than what it is set to.

[cdheller]

I know its not exactly what you are looking for in terms of pressure range but natural gas and propane regulators for houses and commercial use vent.
not a whole lot when the service side get's higher but some ,
hook them up backwards there all vent and no supply .
there is some adjustment in them you probley want to google propane regulators,
natural gas is way low pressure ounces per square inch in some cases

[bluerussetboy]

i'm not sure i understand what possible configuration your thinking of. but....
on almost every standard homeowner/construction compressor the very first component after the compressor air tank is a shut-off valve, not a regulator. these resemble regulators in function somewhat but they actually shut off the power to the motor. some are diaphragms, while others may be poppet valves. almost all of them are spring loaded and set to 'trip' at a certain psi.
on some of the heavy duty framing compressors that run all the time the shut-off valve has been replaced with a bleed off valve. it is basically just a pop-off valve that 'floats' at a preset psi. sorta like treading water.
usually on air compressors it is that last regulator that dumps the excess air.

[jimmy101]

Comparison (with diagrams) of single and double stage regulators.
These drawing don't show vents but I think you can imagin how they would be setup to include a vent.

For the single stage regulator;

1. When the outlet pressure is below the set point (set by the screw+spring) the diaphram flexes down and pushes open the poppet valve to the main cylinder. In the regulation mode the valve doesn't act like a diaphram valve, instead the diaphram operates the poppet valve.

2. When the outlet pressure is adjusted downwards the diaphram moves up, the poppet valve is closed and the excess pressure vents through the spring housing when the diaphram lifts off of its seat. In the venting process the valve acts like a standard diaphram valve.

... natural gas and propane regulators for houses and commercial use vent.

Really? I would be very surprised if a natural gas regulator vented to the environment. Sounds way to dangerous because of the explosion hazard. If the vent mechanism ever sticks open you are dumping natural gas into the building. Since the regulator for natural gas is never changed (are they even adjustable?) why would it even need the capability to vary the downstream pressure?

[cdheller]

... natural gas and propane regulators for houses and commercial use vent.

[/quote]Really? I would be very surprised if a natural gas regulator vented to the environment. [/quote]

I guess look at the reg next to the meter at your house

[/quote]Sounds way to dangerous because of the explosion hazard. If the vent mechanism ever sticks open you are dumping natural gas into the building. [/quote]

As far as I can remember a regulator vent is not allowed inside buildings per plumbing codes.
regulator vents are threaded to run a vent pipe to the exterior.

[/quote]Since the regulator for natural gas is never changed (are they even adjustable?) [/quote]

If a buildings equipment is changed and exceeds the capacity of the piping going from low to medium pressure thou the existing piping ,then regulating it down to low at the equipment saves having to re pipe the building.

adjustable? a couple of ways ,screw in or out for minor, different colored springs for bigger changes

[/quote]why would it even need the capability to vary the downstream pressure?[/quote]

My guess would be expansion .
coming from ground temp to a warm building or to rust covered pipe on a roof would be more than a few degrees difference
maybe because control valves start to blow out at 15 psi,or the approved isolation valves are only rated at 5psi.

[iknowmy3tables]

a sorry for the late post but the poppet thing is the part that I'm thinking of based on the diagrams jimmy posted, however it don't say how exactly the poppet works