Fire Pump 10-Pipe-Diameters from Valve or Tee?

8/14/2020

I have a horizontal split-case fire pump, with suction taken from the header. The distance from the flange of the tee to the pump flange maintains the minimum 10-pipe-diameters as required by NFPA 20.

However, is the 10-pipe-diameters measured from the flange of the gate valve (OS&Y vale) or from the flange of the tee?

I received a comment from a consultant that stated the 10-diameters is to be measured from the OS&Y gate valve flange.

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7 Comments

FIREPE25

8/14/2020 10:17:59 am

I assume you are talking about the requirements for change in direction? If so it is from fitting change in direction to the fire pump suction flange.

Glenn Berger

8/14/2020 10:46:29 am

Concur with FirePE25 - The intent of the requirement is to ensure that the is laminar flow at the pump suction.

franck

8/14/2020 11:07:49 am

from the tee (change of direction)
no doubt possible
the advantage of the gate valve is that it is like having no valve, the distance is therefore not to be calculated from the valve
otherwise the 10 x diameter should apply to all pumps with a gate valve on the suction side

Louie Lincoln

8/14/2020 01:23:49 pm

I agree for all of the above reasons. It appears that the inspector in question has a problem interpreting what he reads. This happens too frequently.

Colin Lusher

8/14/2020 01:47:12 pm

Concur with the others in saying it is from the change in flow direction, so likely from the tee.

But please note; the 10 diameters ONLY applies if the tee or elbow is oriented horizontally, along the direction of the pump shaft. If the branch of the tee/elbow comes in vertically from above or below, and is perpendicular to the pump shaft (parallel to the suction and discharge flanges), then you don't need to maintain the 10x diameter distance.

radhakrishnan

8/15/2020 12:16:11 am

i agree with all the replies, the 10 x dia. should be from the TEE only for horizontal suction connection, it is fairly a thumb rule for the Inspector to check physically at site for conformity of suction side. Gate valve in suction side has low or negligible pressure loss. More over in India we follow a suction pipe velocity of 1.5 m/sec @ 150% flow, which also meets the suction pipe size with minimum pressure loss irrespective of suction orientation for positive suction head.

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