Hello everyone, I have a a single s

[abdi mulu]

Hello everyone, I have a a single stage pump which deliver 89 L/s at head of 113m and the pump is not start unless you close a quarter of gate valve through suction side.why does this pump refuse to start unless its quarter valve is closed through suction side

 

[LittleInch]

Dunno.
How about you provide a diagram with some details.

What do you mean by "refuses to start"?

No flow? No pressure?
Trips the motor?
Didn't go round?

What's on the auction side?
Do you have flooded suction or??
Is there a suction lift from lower than the pump?
Is the pump new or has just started doing this?

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

 

[abdi mulu]

#littleinch, thank you for your response
For your questions when the the gatevalve through suction side opened fully the pump not start running and it trips the motor. But when the gate valve through suction side is closed by 1/4 of full close the pump will run. What is the reason for such cenarios.

 

[LittleInch]

Again more details needed like motor size, what your ACTUAL flow and pressure is when operating.

Could be you are running off the end of the curve on the right and pulling too many amps.

So what you're doing is throttling the pump. Just a bad way of doing it. Try using the discharge valve instead. Close the valve, start the pump then slowly open it until you do the required flow.

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

 

[FMJalink]

Hi abdi mulu,

As LittleInch all ready mentioned, simple manual start-up of larger pumps is done by opening the discharge valve.
Normally starting with having the discharge valve approximately 25 % open. Exact opening percentage depends on your situation.

Your described problem happens often with start-up of a centrifugal pump having no back pressure /resistance. This could for example be with a transport / booster pump pumping into an empty pipeline. Having no back pressure the pump wants to run to the end of the pump curve requiring maximal power.

Hope this he!ps.

 

[bimr]

Pumps don't produce pressure, they produce flow.

With zero resistance, your pump will provide excess flow at startup. Excess flow will then require more electric power than your system was designed for and then trip the motor.

It is preferred to startup centrifugal pumps against a throttled valve, and then slowly open the discharge valve. You may also consider installing a larger motor on the pump so that the motor doesn't overload on startup.

 

[FMJalink]

Do not know whether the system is equipped with a minimum f!ow by-pass, but when not, I would not like to start up with a fully closed discharge valve with a larger centrifugal pump. Also with no flow (shut off), power enters into the liquid. With larger centrifugal pumps, this one is a bit on the boundary, boiling in the pump can occur quite rapidly. If equipped with a single mechanical, a new start-up with a new mechanical seal can be expected.

 

[crshears]

I see where FMJalink is coming from; I wouldn't want to start a largish centrifugal pump against a fully closed discharge valve either, especially not if the discharge valve is manually operated and I'm going to be the person on the handgrip end of the wheel wrench .

Indeed, in the steam plant where I began my career, the units all had three condensate extraction pumps [CEPs], and with the units off line and shut down it was common [actually, required] practice to have the discharge valve on one of the three pumps only cracked open 10% or so, for operational purposes, to wit:

Following shutdown, the standing water in the boiler would steadily lose temperature [at some factor of the natural logarithmic rate ], and shrink in the process. Boiler top-ups were therefore required . . .

The first step in the top-up process, once sufficient water was confirmed available in the hotwell below the condenser, was to start the throttled CEP, filling and pressurizing all the lines and low-steam-pressure regenerative condensate heaters with condensate, right up to the deaerator's condensate admission point. Then, and only then, would a CEP with its discharge valve fully open be placed into operation, following which the throttled unit would be shut down, and the rest of the top-up procedure ensued.

Upon unit start-up, once the turbine was rolling on steam and accelerating to synchronous speed, the throttled discharge valve would be opened wide and same reported to the turbine/boiler operator. Upon shutdown, once all fires had been pulled and steam consumption ceased, one CEP discharge valve would be throttled in to ~10% open; this was reported to the TBO, and the TBO would place a brightly colored information tag bearing the word "THROTTLED" on the start/stop pistol-grip control switch for that pump.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[pierreick]

Hi,
Why do to throttle the valve at the suction of the pump? weird to me. Risk of cavitation.
You should have a valve at the discharge and Pressure Gauge, valve totally closed or partially for the start up.
Thanks to share with us a PFD or PId .BTW do you have a SOP available for your operation team.
Good luck
Pierre

 

[shvet]

why does this pump refuse to start unless its quarter valve is closed through suction side

Because electric system of your pump is not designed for overload during start of pump. Pay attention to el. device which protects el. motor from overload (installed in motor control room/center). Sorry, I do not know correct name in English. You should talk to a local el. specialist to replace this device with more powerful one or prevent it from turn-off by hands during every time you start the pump.

Be careful with overload of pump motor. You are trying to start pump with overcapacity (suction and discharge valves are fully open what means starting intermittent pump capacity attempts to reach ∞). Starting method this kind of leads to short-term overload of motor during first 5-30 sec. If pump itself and all elements of its el. system are not designed for the starting method this kind of then one day you will face with melting of a weakest element of el. system and some damage of others. Or pump shaft will be broken, or shaft coupling and so on. If your pump has API 610 datasheet then you can check specification in line 57 of datasheet.

Also note:
1/ Pumps have some limits of starts, common industry practice is 1-1.5 k starts per pump life (equals 1 start per week). See para. 6.9.2.14 API 610. By this reason false starts decrease pump life.
2/ Suction line must have flow restrictions as min as possible all situations possible. When you have partially closed suction valve you decreased NPSHA; this leaded to cavitation; this leaded to pump internals damage. Normal industry practice is to use discharge valve for this purpose. Using discharge valve instead of suction one leads to risk of overheating of pump caused by human error but eliminates cavitation and extends pump life. My guess is in the past a manager/supervisor had to deal with pump overheating caused by low qualification of operating personnel and by this reason he/she had decided to change pump start practice to more safe one.
3/ Some manufactures prohibit start of pump with fully closed discharge valve (discharge valve should be partially opened). You should check pump operating manual for proper starting method.
4/ Starting NPSHA often is much less then running NPSHA. By this reason sufficient starting NPSHA is important for pump service life. Cavitation caused by too low starting NPSHA may be the reason of false starts of your pump. See description in chap. 25 Lieberman's Working Guide to Process Equipment.
5/ If pump itself was designed for starting overload this fact does not guarantee a pump associated el. system was designed for overload above running conditions.
6/ It looks like you are lack in basics of centrifugal pump design&operation so some proven handbook might be helpful. You should ask here for an advice.

It is curious why you used consulting by an anonym forum instead of pump operating manual. Comment please.

 

[bimr]

It is common practice to start large capacity centrifugal pumps (such as saltwater circulating pump and freshwater circulating pumps) with the discharge wall closed. If the characteristics curves for a centrifugal pump are examined, it will be seen that when the quantity of water discharged is zero, the power required by the pump is zero or a very small amount.

By starting the pump with the discharge valve closed the power demand made by the pump on the pump motor is kept to a very minimum. After the pump has started and the momentary high motor current demand has stabilized, the discharge valve is opened.

Link

Some bad pump operating practices include:

​

Starting the pump with a discharge valve open.

Link