Incoming nat. gas pressure @ 5.0"w.c.???

Empire_2

Hi everyone, I had a nat. gas valve that would not fire. Furnace min rating was 5.0"w.c. Q; On the gas valve itself in general does or is there a mechanical spring or something that would prevent the valve from opening due to lo incoming gas pressure??? Everything is otherwise OK, HSI, 24 to valve when initiating firing. I guess my Q; is there some kind of safety to prevent the valve from letting gas through if low conditions exist? Tim or anyone else, comments much appreciated.


Mike T.

PS, I thought there was a mechanical safety for lo conditions, but cannot remember. 75k res. rheem, direct fire, glow coil. valve has 24 power. Thanks.

Abracadabra

Have you measured gas pressure?

Lance

Know the supply gas pressure. Too high can destroy some valves, to low will not prevent the electric valve from opening but the pressure reducing controls may not function. Also check for pressure drop when turning on gas flow. I have seen a restrictions cause failures. Propane, natural? A licensed gasfitter saves lives and property. Combination gas valves have an off valve, a pressure control, a solenoid valve, a safety pilot valve.
The key to safe gas work is know all the facts and what should be there and what to expect normal is then troubleshoot safely and figure it out. Caution, any valve that partially opens without full flow can cause unexpected and dangerous combustion or explosion, especially propane which we all know is heavier that air. Low voltage and voltage drop on electric valves can cause partial failures. Valves subjected to high incoming pressure above their rating can rupture the control and make it dangerous.

Empire_2

Yes the pressures have been measured in and out. Inlet =7.6 standing, 6.25 with only furnace running. Although this is not my first dance w/ 30 yrs+ HVAC service was just wondering if a safety of some type is incorporated into the valve. In Buffalo, National fuel has occasional freezing meters and or regulators. I am thinking that I have seen this in the past, but I must be incorrect in my thinking( getting old.... :-). Volume is not a concern in this question, but just though I'd throw my problem out there. I do not mean an additional safety as in LP, but internal on the combination GV. All measurements are currently w/o HW tank in the mix.
In this Rheem furnace aprox. 10 yrs old (spec) max inlet is 10.5"wc, and min is 5.0. I thought maybe I was approaching a non satisfactory gas pressure to the furnace. I did have it fire today after gas Co. gave 8.0"wc as I asked their advice and to check the meter on their end. Since the gas valve is a combination, regulator is designed into the gv and it is a Direct fired application.
Abracadabra, I was so far into my question and forgot to tell anyone that measurements were taken...........sorry about that. Yes used 2 manometers just to get a feel of what the equipment was doing in and out while running. Existing gas line into the house after meter is 1" reducing to 3/4" for furnace and HWT, ultimately 1/2" to feed each. No volume problem on design.
Thanks or responding...


Peace;
Mike T.

Tim McElwain

When you provide 24 volts to the valve it is powered and all valves (including dual seated redundant valves) should open giving full flow at whatever the outlet pressure is set for typically 3.5" W.C. You did it right with measuring both inlet and outlet gas pressure at the same time. We typically talk about a 1" W.C. drop through the valve so an inlet of say 5" W.C. with an outlet requirement of 3.5" W.C. would still be meet.

There is no shut down internally on the valve if there is pressure lower than 5" W.C. you just would not get full 3.5" W.C. on the outlet.

Tim McElwain

Most gas valves today that are dual seated (redundant) if the pressure exceeds 1/2 pound (14" W.C.) the first direct acting solenoid which is designed to open in an upward motion will not open and the system is in a form of lockup until the pressure on the inlet is reduced to less than 14" W.C. Gas valves are pretty forgiving when it comes to working even at very low pressures as the 24 volts will still cause the valve to open.

The servo regulators on these valves operate on sensing a down stream demand (number of orifices and their drill size determine flow) through a sensing port which is built into the outlet side of the gas valve. The sensing port in turn positions the diaphragm in the servo regulator built into the gas valve and that in turn controls internal working gas pressure in the gas valve which cause the valve seat to respond and maintain the regulator downstream set pressure (usually 3.5" W.C.).

Empire_2

Thank you Tim. I don't know where I had that lo pressure inter lock like you stated for hi press, but then again better to inquire that to let it go with out satisfying my imaginary safety control......lol. Actually sounds like a regulator from Hi press gas to low pressure gas such as in industrial heating equipment,......If the diaphragm is frozen and cannot move or has water atop the diaphragm, it cannot act properly to put fourth the out put desired.
How are the classes going? Many new-bee's into the art of HVAC? Thanks again Tim.


Peace;
Mike T.

Tinman

Hey Tim, Back in the day...didn't White Rodgers have a valve that had a cut-out for a low pressure situation? 2 short brown wires that curled back into the valve? Or am I confusing that with something else?

Empire_2

I believe that was just a redundant valve. Although remember that little resistor card that went on the face of the mercury pilot switch?

Mike T.

Tim McElwain

Mike you are talking about the EQSO resistor which was White Rodgers covering their butt on a bad pressure switch on the valves a their Cycle Pilot System. We did not allow EQSO resistors here in RI as we proved that they could cause delayed ignitions. So we required WR to provide new valves under warranty.

Stephen not that I remember. We do now have LP conversions on some warm air furnaces sending a low pressure device to be installed after the gas valve to shut down if the outlet pressure gets too low.

Empire_2

Yes Tim that's the one. I personally did not like the mercury style pilot switch. WR as a whole is not one of my favorite MFG. of HVAC products. Yes we too, got the run around from WR...


Mike T.

j a_2

I do know weil mcclain offers a conversion kit for there old mercury style pilot sw..made by white rogers….In fact there is one in stock at jomar ind. in dedham mass….It changes it to a hot surface ignitor….There is a very easy t/ s procedure available on line….