Can someone please explain the difference between pressure relief valves
and back pressure regulators? They both seem to function the same way
with the same internal structure but a GO (Circle Seal) PR57 adjustable
relief valve cost $79 while a BR3 back pressure regulator cost $569.


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Glenn Ashmore wrote:

Can someone please explain the difference between pressure relief valves
and back pressure regulators? They both seem to function the same way
with the same internal structure but a GO (Circle Seal) PR57 adjustable
relief valve cost $79 while a BR3 back pressure regulator cost $569.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Hi Glen

I'm no expert, but run into each at work. The relief valve, as I know
it, is really not intended for continuos duty, more just a safety thing
to prevent excess pressure in a system. Quite often RV's tend to leak
after they pop once or twice. They usually don't have very good
regulation, when they lift they are designed to stay open for some
amount of 'blowdown', i.e. quickly reduce the pressure behind them to a
value somewhat lower than the set 'cracking' pressure.

Backpressure regulators, on the other hand, are designed to vent
pressure above their setpoint more or less continuously and to a much
finer degree. Think plain old regulator, but on the other end of the
system. In my work they are used to maintain sample system pressures
just above vent header pressures to ensure continuos flow through the
sample system into the somewhat varying pressure of the vent header. Did
that make sense?

Could you use a regular RV to maintain a set pressure in a vessel or
system? Probably, but at the expense of maintaining a steady pressure
and probably with reduced longterm reliability.
--
-----------------------------------------
It's a Linux world....well, it oughta be.
-----------------------------------------

Did you perhaps mean BP3 series? If so page 1 of the Standard Features
Section says " In most systems over-pressures are often released by
pressure relief valves, which are simply on or off with no throttling
control. In contrast to the on or off action of a relief valve, a back
pressure regulator provides throttling action and substantially improves
system regulation." There you have it. By this they mean you have
greater precision of control i.e.: accuracy, repeatability, and
hysteresis (deadband). Circle seal makes some great products but they
are not cheap.

Glenn Ashmore wrote:

Can someone please explain the difference between pressure relief valves
and back pressure regulators? They both seem to function the same way
with the same internal structure but a GO (Circle Seal) PR57 adjustable
relief valve cost $79 while a BR3 back pressure regulator cost $569.

On Fri, 25 Jul 2003 08:08:21 -0400, Glenn Ashmore
wrote:

Can someone please explain the difference between pressure relief valves
and back pressure regulators? They both seem to function the same way
with the same internal structure but a GO (Circle Seal) PR57 adjustable
relief valve cost $79 while a BR3 back pressure regulator cost $569.


If you've got the terminology just a bit wrong it makes sense.

Pressure relief valves do just that - relieve excess pressure from the
system. To the air, to ground, somewhere, anywhere except back to the
system.

Back pressure regulators, in my world, are pressure regulators which
can accommodate pressure build-up and relieve that build-up _back up
stream_.

We use them on dishwasher booster heaters, and most states have now
made them mandatory for domestic use, along with an expansion tank.

The thing is, when your house is empty and no one is using hot water,
the hot water heater still cycles to maintain temperature. Since
raising the temperature of water one degree F can raise the pressure
100 PSIG, the pressure which results from heating the water needs
someplace to go - ergo, the water pressure regulator supplying the
house needs to be a back-pressure relieving type.

The excess pressure is relieved back to the street, which in turn
means that the expansion tank needs to be charged to the same level as
street pressure - otherwise it can't do it's job.

The BORG carries both types of water pressure regulators and several
sizes of expansion tanks.
Cheers,
Fred McClellan
the dash plumber at mindspring dot com

I am well aware of the purpose of both valves but the thing is, the
manufacturers of larger valves claim they are both the same and discuss
both applications for the same valve models. They are just to big and
to low pressure.

This is a water maker, not a high tolerence application. I need to keep
the system between 780 and 850 PSI at 2.5 to 5 gallons a minute. The
variable flow means I can't use a needle valve as the primary pressure
control so I have to either use some sort of regulator on the discharge
end. I also don't intent to spend $600 on one valve when the whole rest
of the system will end up under $1500 including a stainles Cat 241 pump.

I realize that a BP3 will have less histerisis but a 70PSI range is a
pretty big target and the GO PR57 is good for several million cycles. I
am more worried about valve chatter than anything else.


Fred McClellan wrote:
On Fri, 25 Jul 2003 08:08:21 -0400, Glenn Ashmore
wrote:


Can someone please explain the difference between pressure relief valves
and back pressure regulators? They both seem to function the same way
with the same internal structure but a GO (Circle Seal) PR57 adjustable
relief valve cost $79 while a BR3 back pressure regulator cost $569.



If you've got the terminology just a bit wrong it makes sense.

Pressure relief valves do just that - relieve excess pressure from the
system. To the air, to ground, somewhere, anywhere except back to the
system.

Back pressure regulators, in my world, are pressure regulators which
can accommodate pressure build-up and relieve that build-up _back up
stream_.

We use them on dishwasher booster heaters, and most states have now
made them mandatory for domestic use, along with an expansion tank.

The thing is, when your house is empty and no one is using hot water,
the hot water heater still cycles to maintain temperature. Since
raising the temperature of water one degree F can raise the pressure
100 PSIG, the pressure which results from heating the water needs
someplace to go - ergo, the water pressure regulator supplying the
house needs to be a back-pressure relieving type.

The excess pressure is relieved back to the street, which in turn
means that the expansion tank needs to be charged to the same level as
street pressure - otherwise it can't do it's job.

The BORG carries both types of water pressure regulators and several
sizes of expansion tanks.
Cheers,
Fred McClellan
the dash plumber at mindspring dot com



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com