re: How to determine the Pump reverse flow

[TurbineBlade]

Hi,

I have a standby horizontal split case double volute pump in my system. When maintenance is perform in the sytem, there will be some reverse flow. Right now, some design modification is needed in the system which may result in an increase of the reverse flow. I am not too sure if this is a problem as the reverse flow must be sufficient large overcome the static friction and the produce inertia force to turn the pump. How can I estimate the value reverse flow rate limit to prevent the pump from rotate in the reverse direction?

Thanks

 

[BigInch]

Stepenhoff, "Centrifugal and Axial Flow Pumps" has a method to develop reverse flow curves explained. If you're hard up for an estimate, use about 30% of forward.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[abeltio]

the author is Stepanoff

saludos.
a.

 

[Artisi]

You should check with the manufacturer - reverse run-away speed can result in very high reverse rotationial speed
- if fitted with mech. seals - these also need to be checked out.



Naresuan University
Phitsanulok
Thailand

 

[sailoday28]

I believe you will have to complete a reversed system H-Q curve in conjunction with the vendors reversed flow characteristics of the pump.

regards

 

[TurbineBlade]

Hi,

Suppliers appear to have the reverse characteristics curves to predict the torque as a percentage of rated values for a given flow, but indicated this may not be helpful.

The flow necessary to just start it rotating depends on the combined static friction within the pump and driver. It is an inertial characteristic which affects acceleration or spin down times, but not how much torque is required to start motion.

 

[ccfowler]

TurbineBlade,

How much and what is the nature of the reversed flow? Is it more than some minor leakage through a check valve? Are you trying to recover energy from this flow?

If you are just concerned about avoiding reversed rotation of the pump and motor due to a small flow, you may want to consider installing a backstop on the pump or motor shaft.

 

[amorrison]

ccfowler has mentioned "check valve".

Is there a check valve or a manual stop valve (usually a gate valve) in the pump discharge piping?

 

[TurbineBlade]

Hi all,

There are a check valve and a motorized valve at a 6" pump discharge line. However, the concern is that there is also a 1" line with an orifice connected upstream of the check valve and motorized valve at one end and downstream of these valve at the other end. The reverse flow is from this 1" line.

 

[BigInch]

The concern should be if the 6" check valve gets broken or otherwise stuck in the open position.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com