Allowable distance for installation of connections from the suction part of the pump

In order to determine the minimum distance allowed for the installation of fire extinguishing system connections from the suction part of the pump, we will examine the possible conditions of the piping from the source to the pump.

For the installation of fire extinguishing system connections, there are generally four different piping situations for the pump suction pipe path:

1) The pipe enters the suction part directly without any elbow or tee. (Figure 1)

In this situation, the minimum length of the horizontal pipe should be equal to 10 times the diameter of the pipe.

Figure 1 – Suction pipe without any fittings

2) The vertical pipe is inserted into the pump suction using an elbow (Figure 2).

This mode is acceptable because the elbow only changes the direction in the vertical plane, and the diameter of the elbow and the pipe are determined before that.

Figure 2- The pipe enters the suction part of the pump vertically using an elbow.

3) The horizontal pipe is inserted into the suction part of the pump using an elbow (Figure 3).

In this case, due to the change of the water path in the horizontal plane, it is not possible to install an elbow at a distance less than 10 times the diameter of the pipe.

Figure 3- The pipe enters the suction part of the pump horizontally and with an elbow.

4) After passing through two elbows, the horizontal pipe enters the suction part of the pump. (Figure 4)

In this situation, the second elbow (further to the suction part) should be placed at a distance where the total length of the vertical and horizontal pipes is more than 10 times the diameter of the suction pipe.

Figure 4- The pipe enters the suction part of the pump horizontally and with two elbows

In some cases, the size of the flanges connected to the suction part of the pump is smaller than the size recommended by NFPA. For example, the diameter of the suction pipe recommended by NFPA for a pump with a capacity of 1000 gpm is equal to 8 inches, but the flange size of the produced pumps is 6 inches, in this case, reducers should be used to change the size of the pump suction pipe from “8” to “6 used in the system.

There are two common types of reducers in plumbing. (Figure 5)

1) Concentric Reducer: The size change is done evenly around the perpendicular to the cross section. Due to the possibility of air accumulation in the upper part of this type of reducer and the occurrence of problems in the operation of the pump, the use of this type of reducer is not allowed.

2) Eccentric Reducer: Size change is done from one side only.

There is no risk of air accumulation in this type of reducer and it can be installed in the suction part of the pumps.