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DaleAllen

Pressure gauge

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Hello and thank you for your help.

My first post so go easy!:D

I want to put a pressure gauge in-line on a gas forge.

First will a standard pressure gauge work or is there something I should use that will not be bothered by the gas.

Also, am I correct to put it in line before the shutoff?

Thanks again.

Dale

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It's going to depend on whether you are building a forge with a blown or ventri burner.  Venturis run at a lower pressure and you pretty much regulate them with the regulator that is connected to the tank with a POL connector and the pressure gauge goes on the regulator.  The regulator and the pressure gauge go inline before the cutoff valve.  I like my cutoff valve right up near where it attaches to the burner so that I can reach it fast if I need too.  I use the adjustable regulator to adjust the gas flow.

My blown burners are pretty much set up the same way except that I have a needle valve to fine tune to gas flow into the burner.  Of course I have to have a connection to the burner for the air blower.  Everything should be rated for gas.  Look up Wayne Coe's site or High Temperature Tools and Refractories and they have the whole set up you'll need or at least the parts you'll need to construct your connection.

Doug

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Thanks for your help Doug.  The regulator does not have a place for a gauge so I'll put it near the cutoff valve. I just thought it would be nice to be able to tell what the pressure from the regulator is since it is a 0-20 PSI.  The forge is a singe burner that was built by me.  The burner is a venturi setup that works well both outside the forge and inside.  After that was done I took the forge apart and cemented the ceramic bricks together.  I'm hoping that will help keep the flames better contained.

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On a Venturi burner, knowing the pressure is useful, rather than essential, mainly to allow the operator to start the forge, set it to where it was last time it did the same job, and get on with something else while it gets to temperature.

I always used to fit a gauge at the mixer (and still do when I want other folk to see what is happening with the burner), but now use plugged welding regulators on my forges. These have graduations marked on the body so that the skirt of the adjusting knob shows the pressure they are set to. They have the advantage of being built "industrial", with a nice big adjusting knob intended for use by someone wearing heavy welding gloves. 

It sounds like a pretty crude way of knowing the pressure, but there are not many gauges that provide significantly more accuracy/repeatability at reasonable cost. 

I like to keep all of my controls at the gas cylinder end: it's the direction I head if things start going wrong and I don't want to introduce the need to make an extra decision while the midden is hitting the windmill. I'm also not keen on adding weight to the end of the burner. 

There are various different gauges available. As said, very few will offer good accuracy at anything like reasonable cost. I tend to use glycerine-filled gauges with 1/4" bottom connections. These have stainless steel cases with sufficient structural integrity to contain the glycerine and the 1/4" connection is a lot harder to break than a 1/8" one. I have seen 1/8" back-entry gauges, salvaged from the regulators of old compressors, fitted on burners and try to keep my distance.

If I *really* want to know what the pressure is doing, I use a 4-20 mA pressure transmitter and a datalogger, but I'm probably a little more anal than most smiths.

It is worth pointing out that gas flow through a jet does not vary linearly with pressure, but as the square root of the pressure. If you want to double the gas flow, you need 4 times the pressure. Doubling the pressure will give 1.41 times the gas flow and halving it will give 0.707 times the gas flow. 

If you want to spend money to find out what is happening with your forge, you will almost certainly get more bang for your buck by investing it in a decent thermocouple and pyrometer.

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