Flexible Coupling in Pump Suction 2

[DGrayPPD]

Is it acceptable to use a flexible coupling in a pump suction line that runs from a fire water storage tank to a pump house which sits on a separate foundation? We expect the tank to settle .65" initially and another 1.17" over 5 years and the pump house foundation is on piles so it will not settle. I seem to get conflicting answers when doing research. NFPA 20 shows using flexible couplings for strain relief, while other sites say to route my flexibility in the line. My opinion is that if NFPA 20 is ok with it, then I am ok with it. Unfortunately it is too late to make changes to the suction line, but will 2 flexible couplings in the straight run out of the tank be sufficient to handle the settlement? Any opinions would be greatly appreciated.

 

[DGrayPPD]

Sorry, my terminology is incorrect. I meant to say, "to compensate for the misalignment," not "to give flexibility." Didn't want to confuse anybody.

 

[MikeHalloran]

That is along the lines of what I was trying to suggest.


Mike Halloran
Pembroke Pines, FL, USA

 

[QualityTime]

Why are you not using bell and spigot ductile iron pipe or ductile iron with mechanical joints

 

[DGrayPPD]

Client specs call for carbon steel

 

[QualityTime]

I don't think carbon steel will last

 

[LittleInch]

your flexible joint of 2 Feb post should be good enough to remove 1" of movement, but could be with being a little longer.

No need to complicate things here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

Be aware that hoses are not expansion joints. They can handle bending and axial alignment but cannot handle axial movement- they do not stretch and when compressed, the overbraid slacks off and no longer supports the corrugations against internal pressure.

The best way to use a hose as an alignment tool is as a replacement for an elbow.

 

[JohnGP]

To get back to the original query-

...but will 2 flexible couplings in the straight run out of the tank be sufficient to handle the settlement?

Yes, I believe such an arrangement would be suitable, with the joints you originally proposed. You would need to support the straight run of pipe adjacent to each flexible joint, with supports incorporating integral height adjustment so you can follow the tank down.

I'm guessing that the pipe from the tank is about 12", but the joint datasheet should identify the lateral or angular displacement it can handle.

The Victaulic Style 233 joints look all right, but my concern would be the (perhaps long term) ability to maintain a proper seal on the outside surface of the CS pipework.

I'm not familiar with the ball-type joint proposed by Johnny Pellin, but feel it may be a little over the top for this application.

 

[DGrayPPD]

Thank you again to everyone for your helpful responses.

Only reason I proposed the victaulic couplings are because the stress engineer is having second thoughts about the flexible hose. What you do not see in the original picture is that there will be a catwalk crossover (width will be more than likely 3'-0") close to the valve for accessibility reasons. The valve is 14" and the stem is projected to be quite tall. Due to the catwalk, the thought was that placing the flexible hose underneath it could create issues if for some reason the hose ever needed to be replaced and maintence could not get to it comfortably. However, placing it outside the catwalk would create too much load on the 14" tank nozzle. So the victaulic couplings were suggested as an alternative with one presumably close to the tee and another close to the edge of the proposed catwalk.