I've read that gas regulators should not be used as flow control
devices. They are just to regulate the pressure. But I can't
understand why. If I turn down the pressure, will it not change the
flow of gas coming out of the hose proportionally? If yes, then why
can't I use it as a flow control device? This is a general question
for a gas-regulator-hose assembly and not specific to any situation. I
will appreciate if somebody could clarify this for me.
Because it's not designed for that. It's a bit like strangling the flow of
petrol to an engine: that would result in the engine running weaker and
possibly overheating, whereas what you want to do is regulate the delivery
of a correct fuel/air mixture. Or suppose you changed the voltage of
your mains supply; your washing machine wouldn't run just as well, but
slower, it would stop altogether at some voltage.
In the case of gas appliances different but equally undesirable things
In an earlier contribution to this discussion,
Gas appliances are designed to run at a specified inlet pressure. The
appliance itself controls the flow. A regulator drops the pressure from the
mains (or a cylinder) to the level required by the applicance - and produces
a (more or less) constant pressure regardless of flow.
I fear that the replies you are getting are inevitably based upon
a supposition that you are considering doing something unusual
with your mains or bottled gas supply, which naturally raises
If your actual intention is to do something with a supply of some
other gas, the situation is different. Perhaps if you share a
little more, the responses might be more useful.
On Sun, 13 Jan 2008 13:57:28 -0800 (PST), firstname.lastname@example.org
Yes it will - but not necessarily accurately.
Flowrate depends on an unpredictable, but consistent, relationship
between the pressure and the overall flow resistance, i.e. the size of
the bore (other things remaining equal). It's hard to control this if
it's the overall effect of a long thin hose, so it's usual to fit a
single short narrow metering orifice, or else a controllable valve.
Consider a pressure regulator, a big pipe, and a small needle valve -
like a welding torch rig. The flowrate will only depend on the pressure
and the size of the valve. The size of the hose (much bigger than the
needle valve) won't have much effect in comparison.
Now try a long thin hose, a big valve and burner jet, then kink or stand
on the hose a bit. Flow is now heavily influenced by the parts of the
system that you don't directly control and less controlled by the valve
you're trying to adjust.
So so long as you have overall flow resistance that's dominated by a
single stable part of the system, you've got control. This can usefully
be a valve.
If it's only a fixed gas jet (like my propane kiln burner) then you
certainly can use the regulator pressure to control the flowrate. This
is a higher pressure system than oxy-acetylene and the hoses are short