Centrifugal pump protection run against closed valve?
Centrifugal pump protection run against closed valve?
(OP)
HEllo,
Does anyone know hoe to protect a centrifugal pump which could possible run against a closed valve, thus to prevent heating by circulating the same volume of liquid in our case: Diesel.
Thank you in advance,
Scyzoo
Does anyone know hoe to protect a centrifugal pump which could possible run against a closed valve, thus to prevent heating by circulating the same volume of liquid in our case: Diesel.
Thank you in advance,
Scyzoo
RE: Centrifugal pump protection run against closed valve?
Good luck
Ralph
RE: Centrifugal pump protection run against closed valve?
Or you could put an auto-controlled valve in the recirc path. One scheme we have is a recirc valve which is controlled at a setpoint based on total flow (recirc plus normal discharge). During normal operation the valve is closed. If the discharge valve is later closed the valve modulates open. If pump is secured valve will go full open. Then it will be full open at time of next pump start. If full-open recirc inteferes with motor starting time limitations, other controls may be required.
RE: Centrifugal pump protection run against closed valve?
Continuous recirculation is usually only done for smaller pumps due to the energy loss and upsizing required on the pump.
One other alternative is a Yarway (or equivalent) ARC valve if your product is clean. Under normal operation, the valve is closed and only opens under low flow conditions. With an ARC valve, you avoid the need for another flow meter and stand-alone control valve manifold.
If possible, run the recirculation line back to the tank rather than directly to pump suction.
RE: Centrifugal pump protection run against closed valve?
All that being said, proper system design such that the pump won't be deadheaded in the first place is better.
RE: Centrifugal pump protection run against closed valve?
Thank you guys for your advise.
Butelja, I have not much knowledge about instrumentation, what do you mean exactly with electrical horsepower. If the pump is running against a closed valve -> head = 0 m. If I look at the centr. pump curve,then I see that the power usage isn't at its maximum, when head =0 m.
How do you measure "electrical horsepower"?
Thank you in advance.
Scyzoo
RE: Centrifugal pump protection run against closed valve?
Determine what is the minimum flow you want to trip the pump at, estimate the Hp and then determine the corresponding amperage.
RE: Centrifugal pump protection run against closed valve?
One thing you would have to be careful of when setting your current relay... the relation between current and motor output power is fairly linear at high power (near full load), but woefully non-linear at low load. A low-speed motor may have 50% current at zero percent load.
Another thing that comes to mind... the shape of bhp vs flow curve was discussed in recent thread Thread407-27055 . To my understanding, single-stage axial flow pumps will draw the highest current at shutoff. Perhaps in that case instead of undercurrent, we simply adjust the overload setpoint down lower? Other varieties of pumps may have differing shapes of bhp vs flow curves which will require individual consideration when setting your relay.
RE: Centrifugal pump protection run against closed valve?
As you rightfully mentioned, the current vs. horsepower relationship at low loads is very nonlinear. This is the reason for measuring true power [V*I*sin(phi)], not just current. Current monitoring does not work well at all for low power cutoffs. One manufacturer's device for measuring power can be found at: http://www.loadcontrols.com/. An article on power monitoring from another company can be found at http://www.flowserve.com/pumps/technical_lib/index.stm#.
RE: Centrifugal pump protection run against closed valve?
http://www.rainbird.com/Commercial.asp?Page=Product&LinkID=D56E8FD1-A843-488C-9193-FD7774F3CB54&SubCat=F8892584-79CE-4C05-A727-CEC3C16CA389
RE: Centrifugal pump protection run against closed valve?
A flow detector switch (ANSI code: 80) wire it as NO (normally open - closed with good flow).
Install the switch immediately downstream of the pump (before the check valve or any other valve). This means you will use one flow detector for each pump in the same service.
In the control system, add a 10 sec time delay if no flow is detected for 15sec (or a loose wire) the pump will trip.
Note: depending on how critical the service is, you'd like to have 3 switches installed for each pump. and do a 2 out of 3 logic voting in the control panel.
Hope this helps.
saludos.
a.
RE: Centrifugal pump protection run against closed valve?
Is the power expressed by VISin(phi)or VICos(phi)?
Regards,
RE: Centrifugal pump protection run against closed valve?
OOPS, my mistake for posting too quickly. Yes, power is expressed by V*I*COS(phi), NOT SIN(phi).
RE: Centrifugal pump protection run against closed valve?
RE: Centrifugal pump protection run against closed valve?
Simon