Gas Flow Control and Regulators

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.
Reply to
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 would happen.
Reply to
John Stumbles
Thanks for your reply. So what kind of flow control device should I use? Some type of valve? I just want to get a steady flow of gas in a compartment by inserting a hose connected to a gas supply.
Reply to
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.
Reply to
Roger Mills
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 safety concerns.
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.
Reply to
Chris J Dixon
On Sun, 13 Jan 2008 13:57:28 -0800 (PST), wrote:
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 and fat.
Reply to
Andy Dingley

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