clogged suction or discharge pump linr

[Thuba]

Say l have a clogged discharge line, the pump current drawn by a pump should not drop; just as starting a pump with discharge valve closed (0 flow). Also a clogged suction line shouldnt result in less current drawn since flow is low. l am confused as to how both cause increased current drawn?

 

[EdStainless]

Think about power.
Pumping against a closed line obviously requires more power.

 

[Artisi]

Please define clogged.

 

[Thuba]

Please define clogged.

blocked

 

[Thuba]

Please define clogged.

block

Think about power.
Pumping against a closed line obviously requires more power.

ok thanks, how about a clogged suction, needs more power? l want to have a way to know if its the suction or discharge clogged, by just measuring power

 

[LittleInch]

Say l have a clogged discharge line, the pump current drawn by a pump should not drop; just as starting a pump with discharge valve closed (0 flow). Also a clogged suction line shouldnt result in less current drawn since flow is low. l am confused as to how both cause increased current drawn?

This doesn't make sense at the moment.

Pump current should not drop?? Drop in realtion to what? Running current? start current?

Less current since flow is low?? Less than what?

I don't think you're going to find out from power what is going on. Listen to the pump. If the inlet is blocked it will be cavitating like mad. If the discharge is blocked it wont.

You are better off using pressure guages...

Or just removing the blockage from both ends

 

[innovativepumps]

It would be helpful for all if you stated the type of pump in question and the min/operating/max "current" for your application. If its a PD pump, yes, the current will increase as the pump struggles to maintain the volumetric displacement. A centrifugal pump can still output higher pressure albeit at a lower flow rate but depending upon how sensitive your current measurements/thresholds are you might see an increase. Are you attempting to determine clogged status based upon pump current drawn? Obviously the goal for pumping is to not block the inlet or outlet line, measuring differential pressure across a strainer/filter or monitoring pump flow rate/pressure would be belter ways to detect line/element fouling.

 

[TenPenny]

Look at your pump curve.

If you're talking about a centrifugal pump, typically, the shut off head power (power pumping against a blocked line) is NOT the highest power point. Tyically, it's at run out (pumping against a wide open discharge).

For some, such as axial flow pumps, it will be at shut off.

You need to look at the power curve for the actual pump you are investigating.

 

[TenPenny]

Think about power.
Pumping against a closed line obviously requires more power.

Pump curves would suggest otherwise.

 

[Artisi]

Pump curves would suggest otherwise.

Unless very mixed-flow or axial.

 

[TenPenny]

Unless very mixed-flow or axial.

Which is why my earlier comment points this out.

 

[Doug Hunter]

My first question is: is the pump a dynamic pump or a displacement pump? My second question is the same as LittleInch: what is the baseline to which you are comparing?

 

[TugboatEng]

This depends on whether the pump is a positive displacement or turbine/centrifugal. Remember, pump power is flow * pressure.

In a centrifugal pump, the pressure produced is a function of mass and velocity. At constant speeds, the pressure changes little based on flow conditions. When the discharge is restricted, flow drops and pressure doesn't change. This means the power of the pump is reduced.

If you restrict the suction you get cavitation which reduces the mass and cause the pressure to drop. Flow may also drop. Under cavitation the pump power drops rapidly.

For a positive displacement pump, flow volumeis constant. Any restriction on the discharge causes pressure to rise and pump power to rise.

A restriction on the inlet side reduces the volume. The same volume enters the pump but under cavitation conditions a portion of that volume is now condensable and will condense before it leaves the pump. This reduces flow and therefore reduces pump power.


Never restrict the suctions of your pumps as you can get cavitation regardless of pump type.

 

[Artisi]

Which is why my earlier comment points this out.

Sorry, missed that one.

 

[crshears]

OP: more information yields better answers!