3 replies to this topic

[Neelrahs2006]

Hi,

I wanted to ask anyone if they know what's the criteria to re-rate an old positive displacement pump (in another simple word is what should i be looking at to re-used an old positive displacement)?

If i have a new sets of flowrate and different destination for the old pump, what criteria should i use to evaluate if i still can use the pump or change it?

This is especially for positive displacement pump of the Rotary type.

Thank You.

Regards,
Shar

[Art Montemayor]

Shar:

There is nothing that you can do to “re-rate” a positive displacement pump from a process standpoint. And from a practical, mechanical standpoint there is little you can do except perhaps reduce the rpms.

The usual thing that is done (and I’ve done this countless times with gear and vane type of PD pumps) is to disassemble the pump and check out all the clearances and its physical condition. In a PD pump it is the clearances that make or break the successful operation of the pump. If the wear is significant, it is then a matter of reconditioning the working parts or replacing them. Many times, if your location and working conditions warrant it, you can totally recondition the pump. In the USA and other so-called developed countries, the cost of labor is so high that the replacement of the pump with a new one is the most economic option.

If you plan to reuse an old pump, you should disassemble it and check it out internally. A bench capacity test should also be done to verify its performance. If the pump passes those tests, it should be ready to work.

[Neelrahs2006]

Thanks for the reply Art.

This means, i can reused the pump, but i have to check the pump internally and if the pump doesn't have significant wearing, the only thing i can do is to reduce the rpms. If the new condition falls within the current rpms pump curve, hence i can still use the old pump (there is some pump curve from the vendor, but each curve is with a fixed rpms)?

[Art Montemayor]

Shar:

I wish I could help you more on this topic, but you make life difficult for yourself and me when you fail to tell us ALL the basic data of your application.

We don't know the type of pump - internal gear? external gear? vane? lobe?
We don't know the manufacturrer.
We don't know the rated rpm.
We don't know the rated capacity.
We don't know the new capacity - higher or lower than the rated?
We don't know the fluid.
We don't know the discharge pressure.
We don't know the driver type.
We don't know the size of the driver.

I know how I would tackle this problem, assuming some of the above information we are lacking. I would call the manufacturer and get his predictions for the required speed on the pump with the desired new capacity. Then I would make a pumping stand in my maintenace area. I would put a pulley on the pump that corresponded to the pulley on an electric motor. I would size the v-belt drive such that it would yield a pump flow about 110% of the desired. I would use a test fluid as close to the actual fluid in viscosity as I could. I would run the pump and measure the pumped rate at the desired pressure.