gas pressure limits

jhansen

I recently installed a new weil mclain ultra 750 which has high and low gas pressure switches.  It is tied into a two inch gas main running at 5 to ten pounds and then stepped down to seven inches with a regulator at the boiler.  However there is also a three million btu lgb boiler tied into the same gas line.  When the lgb shuts down the high limit trips on the ultra.  Is there a more sensitive regulator out there that can take care of this.

Joe H.

Jean-David Beyer

Is there a more sensitive regulator

I am not a professional heating expert, especially with gas. So bear this in mind. I do have experience designing control systems (mostly electronic) though.



So the first thing I would consider, if it is practical, is to run separate gas lines from the gas source to the two different boilers. Chances are that this will not be acceptable because of cost.



The second thing I would try, if the LGB boiler is closer to the supply than the W-M, is to put a step-down gas pressure regulator as close (but downstream) to the big boiler as possible to step the gas pressure down from the 5 to 10 pounds to about 2 pounds. Then allow the regulator in the W-M to take it down to the 7" or so that boiler requires. The theory being that the first regulator will smooth the pressure transient caused by the LGB boiler switching on and off to something the existing regulator can handle. Trying to do it all in one regulator can cause stability problems. Remember, this is all theory that definately applies to electronic systems, and I suspect it applies to gas systems as well. But you should check this idea out with a gas professional (e.g., an expert at the gas company).

eluv8

gas pressure switches

Do not put 2lbs of gas to the weil mclain, max 14" w.c.



How close is the secondary regulator to the weil mclain and LGB. It needs to be at least 10' equivalent from the boilers. I am not aware of a diaphragm regulator that is fast acting.

bob_46

Reg

You need a positive downstream lock-up regulator.

Jean-David Beyer

I meant before the 7-inch pressure regulator ...

... at the entrance to the W-M.

Tim McElwain

Is the large burner

piped in before or after the WM?



Sometimes all you have to do is increase the pipe manifold to the smaller unit for about 10 feet to a size equal to or greater than the LB pipe size.



My procedures are to set the operational gas pressure from the rating plate of equipment say 3.5” WC. The Low Pressure Switch is then adjusted with the burner running, slowly close the main gas train manual shutoff cock and adjust the switch to open its circuit when the pressure falls below its normal value. The burner will shut down. Open the manual gas cock to full open position and manually reset the Low Gas pressure Switch. The burner should start.

 

As to the High Pressure Switch. With the burner running, adjust the switch to a point where the switch opens its circuit. The burner will shut down. Manually reset the switch and readjust the cut out point to be made at the normal operating pressure, but to open if the pressure goes slightly above normal.

 

Tim McElwain

Sorry for the

large print!