Pressure Relief Valve Installation

[TomFitz]

We have constructed a complex with mechanical room containing 2 hot water boilers operating at approx. 30PSI.
I have noticed that the contractor has piped the pressure relief valve (of both boilers) to relieve to the floor.

As far as I remember, I believe that these must be piped to a drain (which is about 20 ft. away).
I was looking for some reference to code or standard that would give the proper installation practices.

My Question:
1. Is it mandatory that the Pressure Relief Valve be piped to a floor drain. ?
2. Is it allowable for this contractor to use more than two elbows to reach a floor drain?

(some where I remember seeing that more than one elbow can not be used on the discharge side as this could impede the release pressure)..

Thanks for any assistance..

Tom

 

[gr2vessels]

Hi Tom,
I'm having trouble believing that the contractor might be forced to build you a drain system in the floor, if any code would make that piping mandatory and incidently you might not have the floor drain. Also, would you expect him to pipe away your drain pipe to the nearest floor drain 100 ft away, if that's the only one available? Because of a Code recommendation? By the way, some people use to add on their steam pressure relief line not only more than 2 elbows, but silencers also.
Cheers,
gr2vessels

 

[TomFitz]

We are not attempting to force the contractor to build a drain system in the floor. The fact that the drain (which is nearby but not directly accessible)is not closer for the PRV drop to empty into it would not be the fault of the contractor but of the designer.
If anything, I am attempting to help the contractor pipe it to the drain, but I don't want to offer a suggestion that would be against any codes or standards. (by suggesting that he use three more elbows in extending the discharge to the drain)

In my research I did com upon ASME standard - HLW-800 "SAFETY RELIEF VALVES" - which states:

HLW-801.7 Safety Relief Valve Discharge Piping
(a) When a discharge pipe is used, its internal crosssectional area shall be not less than the full area of the valve outlet or of the total of the valve outlets discharging thereinto, and shall be as short and straight as possible and so arranged as to avoid undue stress on the valve or valves.
When an elbow is placed on a safety relief discharge
pipe, it shall be located close to the valve outlet.
(b) The discharge from safety relief valves shall be so
arranged that there will be no danger of scalding attendants.
When the safety relief valve discharge is piped
away from the water heater to the point of discharge,
there shall be provisions for properly draining the piping
and valve body. The size and arrangement of discharge
piping shall be such that any pressure that may exist or
develop will not reduce the relieving capacity of the
relieving devices below that required to protect the water heater.

The above speaks "When an elbow is placed on a safety relief discharge pipe" (singular - meaning one elbow)but still, I find this a little vague..

Thanks for your comment..

Tom

 

[dcasto]

The reason the code says "When an elbow is placed on a safety relief discharge pipe, it shall be located close to the valve outlet." it is refering to the previous sentence, in piticular the part about stress. When the relieving product makes a 90 deg turn, there will be forces on the valve and the farther away the more torque or bending moment on the relief valve.

As for going to the drain, thats not required. The rules says vent the steam so no one gets hurt, so down to the ground and let it cool off down there. Then it says the line and valve must drain, so that means the exhaust lines must slope away from the valve.

You could ask if the location of the exhaust is close enough to the ground and away from where people could reasonably be working or standing (heck they could be cleaning the drain when the relief valve goes off).

 

[Keith53]

As a boiler inspector, I can only speak for my state jurisdiction...Yes, we all inspect to ASME code, but sometimes local codes are also involved.

It is perfectly acceptable to direct the safety valve discharge simply down over the side of the boiler away from front or side where operator might stand...Then about a foot above the floor have the escape piping terminate above a funnel drain that is then piped along the floor to the floor drain.

Keep escape piping as short and light as possible(or support it) so that it doesn't flex the valve body and cause it to bind and thereby not operate at set pressure.

 

[TomFitz]

Thanks Keith,
I think that is the way we will go.

....and thanks to all for their input..

Tom.....

 

[wb1]

From my experience - reliefs are only required to run to a drain if they pose a hazard if they are left to drain to grade. Liquids are normally routed to a safe location so that no one is injured when the RV is activated. Gases can be routed up above personnel height so that again no one is injured.