Pump force calculation

[JohnWeal]

Good morning All,

I have a pump with a total head of 19.4m (63'-7") and a flow rate of 1571 litres/second (24901 GPM)

The pump discharge flange is 700mm and there is a reducer to increase the size to match the riser pipeline of 800mm diameter.

The max rotational speed of the pump is 750 RPM.

What is the calculation or formula to determine the forces on the pump?

Regards

John

 

[BigInch]

Apply gravity.

Seriously, what forces? Short circuit torque, fluid pressure, pipe thermal loads?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[JohnWeal]

Hi BigInch

Thermal loads are very low, but it was the fluid pressure I was thinking of. I have read a few posts on this forum and it seems there are no forces to worry about.

The discharge pipe (800mm diameter) has a horizontal length of approx 8 metres and then a 'duckffoot' bend to turn the pipe up to a 12m high chamber. I calculated the load on the bend in the conventional way but wondered if there was any kind of back-pressure on the pump.

Regards

John

 

[BigInch]

I think that technically you are right in your thinking about unbalanced pressure forces, such as pressure fields entering and leaving elbows and jointed pipe bends, etc., but in continuously connected, especially welded, pipe, it is usually assumed that unbalanced internal pressure forces in the pipe are counteracted by shear and tension forces in the pipe walls themselves that eventually dump them into surrounding soil, or via friction on pipe supports in above ground lines into pipe supports and sleepers. In the case of pumps, that would be accomplished by both pipe distributing such loads to nearby pipe supports, or by the anchor bolts of the pump itself. Anchor bolts of pumps should be sufficient to resist torque loads on startup, which in most cases will be greater than the forces actually allowed on the intake and discharge flanges of the pump itself from connecting pipe. They should also be sufficient for unbalanced pressure forces, but I can't tell you for a fact that such is a specific design condition of pump manufacturers themselves, even though I would like to be able to tell you so. In any case, I have never designed the pipe to balance pressure forces on the pipe-pump interface, say, resulting from the suction pressure in the Y direction and discharge pressures in the X direction.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek