# (OT?) Equivalent drill size for LP Gas (Propane)

I'm converting a natural gas salamander-type heater (150,000 BTU/hr) to propane. The current NG version has a regulator in it, while the equivalent
LP version (from the same manufacturer) does not. The simplest way to convert this opne is to leave the regulator (it's a 1/2 PSIG input, 3"-6" adjustable output gas regulator) in there so I don't have to add a length of pipe, and to use a standard high flow, low pressure LP gas regulator (11") to supply it. The orifices in the NG version are 10 #40 radial holes. What I want is a place to start with an equivalent hole size for LP gas. I haven't yet looked up the chemistry of propane to try and work out what an equivalent stochiometric flow should be, nor the physics (viscosity and density) to see what I should expect for flow rates. Since the inlet LP pressure to the orifices will be the same as the current NG inlet pressure, I can't work it out from the usual tables. Any of you guys know a simpler way to approach this? Thanks.
--
Bob (Chief Pilot, White Knuckle Airways)

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When I converted some old space heaters from NG to LP, I went to the local LP supplier who had a cross-reference table from BTU rating to orifice size for both NG and LP. He had some minimal brass orifices which he drilled out to the proper size.
On Mon, 6 Mar 2006 18:44:21 -0500, "Bob Chilcoat"

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I don't know much about this but I was under the impression that the different pressures were a requirement to obtain the proper gas velocities for differing burning speeds of the gases. In other words, to prevent flashback or lifting of the flame from the burner. I think this is why you have to have a certain pressure range for each gas to obtain proper velocity and then use the orfice size to control the amount of gas. Small variations in pressure are used to fine tune the amount of flow. Just like you can operate a given size welding tip only within a small range of gas flow rates. I am sure others know lots more about this.
Don Young

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