nat gas problem

Larry_7

First of all, regs ain't my field so forgive me launching into the unknown. Maybe the gas co. reg hunting so severely that it locks up on the boiler shutdown, then the WH sucks the available pressure before the reg senses and trys to correct for the loss. The reg may have time to compensate for the boiler on start-up depending on the time allowed to prove flame. Far-fetched musing to be sure. Understandably the poor reg is being asked to supply 2,440 CFH (about 41 CFM) for a while and then slam on the brakes to 40 CFH (about 0.6 CFM)with minimal downstream fluctuation. Some careful consideration in reg selection is an understatement. Some serious pressure readings are in order observed while cycling the boiler, WH control outlet/inlet and the same on the boiler. Fuel line press at equipment inlet with everything on and off, press at outlet of meter or supply reg. My little pocket reference on pipe capacity stops at 200' and says 4" carries 4600 cu. ft./hr with a 0.5"wc drop. Of course adequate comb/vent air should be verified. Loss of pressure in a properly sized fuel line would seem to hedge back toward the source. I may be way off base but my gut says the gas guys are gonna be doing some head scratching too. Already mentioned--how long has this been going on and/or what has changed? Some of my co-workers are reg heads. I'll toss it in tomorrow and see what comes out. Also, if you find out what a hammer valve is do tell.

Good Luck,

Larry

MIKE6

Nat gas problem

I have a 2 mill Btu powre burner.Supply pressure 6 inches WC.Also on the 4 inch supply is a 40k btu hot water heater.This is in the same room as the power burner.If the water heater is on and the power burner shuts down the burner flame to the water heater goes out.The pilot then relights the flame.I saw this happen.The problem is the pilot goes out onthe water heater sometimes.I'm thinking of installing a in line regulator,even though the water heater has a built in regulator.It almost seems like it needs an expansion tank.The gas co said I need a hammer valve.I nor anyone I know has ever heard of this.Any ideas?
Mike

Unknown

Do not put another

regulator in for the water heater it will not help the situation. Did this just start or has it been doing this for sometime? If it has just started has something been changed in this boiler room. I worked for the gas comapny for 28 years I never heard of a "hammer valve". I would ask them to be more specific as to what they are talking about. It sounds to me like this boiler is sucking the pressure down in the gas line then when it is off it comes back up. It could be the way it is piped in. There is also the possiblity of a negative pressure problem in the boiler room. What would an expansion tank have to do with gas pressure???

MIKE6

Tim The power burner is on ,the water heater is on.The power burner shuts down.This causes the main burner flame to the water heater to go out.It is like there is too much pressure applied to the gas supply for a second.The flame pulls away from the water heater burner like it is over gased.I was thinking the power burner vaalve closes and the gas pressure bounces the regulator on the water heater.Hence something like an expansion tank on the gas pipe to absorbe the shut down.
Mike

Jack_23

Air side

Tim is correct in suggesting a possible air side problem. You have such great mass air flows to 2mil burner that it can easily influence a 40Kbtu nat'l draft burner. Has anything changed in the air side in the room. I'd look at a Tjernlund Enforcer for the Comb air. It is the only one with positive safeties.

[Deleted User]

Had the same

Problem about 10 years ago.Had a power burner with an A.O.Smith burkay heater off the same gas line.Every time the burkay heater was on and the power burner came on it would starve the heater of gas and knock the pilot out.Gas company checked and said gas line is sized right.(2 inch) What I had to do was,on the power burner(power Flame I think) was a set of contacts that was powered when there was a call for heat and denergized after the burner started.I wired a relay to the set of contacts to open the circut to the burkay heater when the boiler started and after it fired the relay would drop out and start the burkay heater.That solved the problem.Now there could have been some other reason that I was having problems with this but like I said,the gas company clocked meter and checked line size and said all was good.This was about 10-12 years ago,,,,,Hope this helps.....

Larry_7

The reg head says

> First of all, regs ain't my field so forgive me

> launching into the unknown. Maybe the gas co. reg

> hunting so severely that it locks up on the

> boiler shutdown, then the WH sucks the available

> pressure before the reg senses and trys to

> correct for the loss. The reg may have time to

> compensate for the boiler on start-up depending

> on the time allowed to prove flame. Far-fetched

> musing to be sure. Understandably the poor reg is

> being asked to supply 2,440 CFH (about 41 CFM)

> for a while and then slam on the brakes to 40 CFH

> (about 0.6 CFM)with minimal downstream

> fluctuation. Some careful consideration in reg

> selection is an understatement. Some serious

> pressure readings are in order observed while

> cycling the boiler, WH control outlet/inlet and

> the same on the boiler. Fuel line press at

> equipment inlet with everything on and off, press

> at outlet of meter or supply reg. My little

> pocket reference on pipe capacity stops at 200'

> and says 4" carries 4600 cu. ft./hr with a 0.5"wc

> drop. Of course adequate comb/vent air should be

> verified. Loss of pressure in a properly sized

> fuel line would seem to hedge back toward the

> source. I may be way off base but my gut says the

> gas guys are gonna be doing some head scratching

> too. Already mentioned--how long has this been

> going on and/or what has changed? Some of my

> co-workers are reg heads. I'll toss it in

> tomorrow and see what comes out. Also, if you

> find out what a hammer valve is do tell.

>

> Good

> Luck,

>

> Larry

Larry_7

Reg man says

Careful reg setup at the meter should correct the problem. The existing reg is unable to compensate for the wide gap in demand in a timely fashion. By the time the reg senses the low flow after boiler shutdown and attempts to compensate, it's too late to get the goods to market. In his experience, the solution has been to use a pilot operated reg at the meter with careful consideration given to the downstream sensing line location. According to him, another solution would be for the gas co. to set the meter and reg to deliver elevated press and cut the press again at the equipment. The first scenario would be preferrable due to the cost of setting up the meter and reg and the cost of indoor regs with associated venting to outdoors.

Good Luck

Larry

Unknown

I think the problem

may be that the system regulator can not react quickly enough to compensate for the shut down of the large input boiler. You are then getting a surge in pressure at the water heater. Is the water heater piped in on the same line as the boiler? Is it before or after the boiler? What you need is someone from the gas company to look at this set up and advise you as to a possible regulator change on the line to react differently to the boiler shut down.

I have at times in the past run into a similar situation. We had a seperate line run to the water heater with its own gas company regulator to protect against surge. That is different than putting a additional appliance regulator.

I have been real busy but let me get hold of someone here locally at the gas company and see what they have to say. I will get back to you. In the meantime Larry may have the answer.

Ian_2

Hmmm...

interesting problem Mike. Be sure to post the cure you will no doubt find. You haven't given any numbers as far as pressures are concerned, this is probably a good starting point. I would have a tendency to start at the meter set, use that as your benchmark, then go to the water heater. Check it solo, then bring on and off the connected loads. If as you have indicated its a overpressure problem and you are using a liquid manometer, you may want to have some spare fluid. I'm thinking gas is compressable, as well as springs and diagrams in the boilers and hwt would buffer this kind of "bump".
All the best to you Mike

MIKE6

Here s the deal

The gas co.told the city,over a year ago, that the main needs to be extended to feed from an elevated pressure main.The city which owns the property I worked at did not listen to them.Last year it worked ok mild winter.Now it locks out on low pressure,during high demand time.After the main and regulators are in place it should work.If not the water heater needs to be piped from the meter instead of teeing off of the power burner supply.OH yea the gas co is billing the city for the main hook up.This was the real problem.Thanks for your input guys.
Mike

Glen

I agree that you should start with the service reg at the meter - while it is probably correct for the power burner - it's response time would be too slow for the water heater - hence the brief flame lift off. By putting a slack tube or Magnehelix on the supply line you should be able to witness a small pressure bump. Solution? Probably a separate supply - as to the hammer valve - ????

Art Pittaway

Question about time

Does a gas valve that is that big have an adjustable shut down time. Like a large water control valve has an adjustment to shut it down slowly I can't imagine that a gas valve would slam shut. Gas is a fluid and anyone that has worked with steam knows you don't slam the valve shut.
Also, could the combustion air damper (if it's mororized) be adjusted to allow a spike in the room pressure somehow? Shut to soon and create a vacuum.???
Art