pump discharge pressure and flow rate

[veoteveo]

To avoid calculations of pipe lenght, elbows, pipe id etc I placed a pressure guage on the discharge of my pump.

The guage reads 4.26Bar, approx 43meters, approx 130feet

Is it correct to infer this is the pump head loss ?

Fluid is DI water at 20C
Pump is 20Hp data attached.
Hz pump running: 50Hz
Pump rating 3500Hz

The pump forces the water through a loop back to the tank that feeds the the same pump, closed loop during pressure testing.

A vortex meter indicates 100 liters per min. I feel that this value incorrect, any observations confirm that the value of the vortex meter is incorrect?

 

[TD2K]

By the pump head loss, do you mean the piping losses from the pump discharge where you have this pressure gauge back to the pump's suction?

The pump's head is the discharge pressure minus the suction pressure. Depending on the height of water in the suction tank, that can be close to a bar pressure plus whatever pressure the tank runs at.

I can't really say whether the flow is correct or not from the information you've posted. What makes you think the flow is wrong?

 

[Krausen]

That would not be a correct inference. Your discharge pressure reading is the head supplied by the pump to your closed system. Find the pressure in the pipe just upstream of when it enters the tank. At this point you can determine your head losses by factoring in any elevation and/or pipe diameter/velocity changes using Bernoulli's/Conservation of Energy. Make sure your pump is at a steady rate when you take your readings.

 

[ElSid1]

Head does not equal pressure from a gauge. There are viscocity factors etc. Pressure should ALWAYS be converted from xxx to head. You should measure the pressure off of the pump ports. If there is a vertical distance between the gauges, that needs to be added (Krausen touched on this)

 

[veoteveo]

I did calculations and my gauge readings in psi are what i would expect with media i am pumping.

Thus please note that the pump discharge pressure can be converted to feet of head, all in all if you know data on the media your pumping and pump characteristics.

your advise was very helpful!

Sanitary Friction Piping Loss Calculator Results


Based on the information you provided, we have calculated a friction loss of
42.92 m or 4.2 bar*.


Flow Rate: 280 (LPM)
Viscosity: 1 (cP)
Specific Gravity: 1
Temperature: 22° (C)
Tubing Type: Stainless Sanitary Tubing
Nominal Tubing Size: 2 (in)
Tube Length: 200 (M)
45º Elbows: 20
90º Elbows: 20
Tee Flow Through: 2
Tee Flow Branch: 2
Vertical Rise: 10 (M)

 

[TD2K]

So much for being able to avoiding calculations of pipe length and elbows.

If you want the pump head, measure the suction pressure and the discharge pressure, the head produced by the pump is the difference.

 

[ElSid1]

What TD2K said. I got a little ahead of myself, but that is what I meant when I said "You should measure the pressure off of the pump ports" which is equivalent to TD2K's "measure the suction pressure and the discharge pressure"

 

[Artisi]

Your terminology is incorrect "Is it correct to infer this is the pump head loss ?" NO - without getting too academic, this is the total head on the pump discharge which includes friction losses, static head etc etc.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[BigInch]

Pump differential head happens to equal head loss only in a closed loop.

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

 

[Krausen]

"If you want the pump head, measure the suction pressure and the discharge pressure, the head produced by the pump is the difference."

This is only true given a number of assumptions - 1. You ignore your frictional losses, which may or may not be reasonable. In reality, your pump head will be higher than the difference between discharge & suction head pressures. 2. Your pump nozzles are at the same elevation. 3. Your kinetic head energy is equal at both nozzles (same diameter nozzles ... this factor is often considered negligible)

 

[BigInch]

This is only true given a number of assumptions -

1. You ignore your frictional losses, which may or may not be reasonable. In reality, your pump differential head will be higher than the difference between discharge & suction head pressures.
No, or only very slightly, due to differences between suction and discharge velocity. Pipe friction losses do not enter into the pump head equation

2. Your pump nozzles are at the same elevation.
Again no. Pump differential head is indeed the difference between total suction head and total discharge head (assuming small velocities), which includes elevations.

3. Your kinetic head energy is equal at both nozzles (same diameter nozzles ... this factor is often considered negligible)
Not necessarily, but true only if velocities are the same at suction and discharge.




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

 

[QualityTime]

My answer below is very similiar to BigInch:

A pressure gauge and a suction gauge is required is required to determine TDH. If it is under a flooded suction conditon subtract the suction reading from the discharge reading and then add the difference in velocity head between the suction and discharge if the suction and discharge flange sizes are different. If it is under a suction lift condition you will need a suction gauge that measures negative pressure. Add the two gauge readings and then add the difference in velocity head between the suction and discharge if the suction and discharge flange sizes are different. Make sure you make the correction for the gauge readings to the pump centerline datum.

Do a shut in head test and you should hit the shut in head point on the curve. Throttle the discharge valve to develop readings and plot it agains the pump curve and tell us what you observe.