4 replies to this topic

[zyy]

Hi. I am asked by my senior to develop a process calculation spreadsheet to calculate positive pump hydraulic. I have a spreadsheet for calculating centrifugal hydraulic developed involving one suction and up to 3 discharge pathways. I think maybe I can modify the spreadsheet to suit for positive displacement pump. May any one help me in which variables I should modify or include in for Positive Displacement pump, like NPSH etc? As far as I know, positive displace pump deliver constant volume regardless the pressure. In the centrifugal pump, we have included the variables of capacity of the liquid to be pumped to discharge pathways. Can I assume that the flow rate of liquid from suction side will be the required pump capacity for positive displacement pump case?

[bmk]

You must install a pessure sustaining valve of spring loaded type after the NR valve on the discharge side of the pump. The pump delivers constant flow rate so long as there is a resistance on the discharge side otherwise it will change with the liquid-level in the suction tank. You can verify this by installing a pr.gage and a rotameter after the pressure sustaining valve. For more details you can refer to:

V.K.Pump Industris p.Ltd.
contact V.K.PUMP INDUSTRIES PVT. LTD. H/O & REGISTERED OFFICE 39-B, Suren Road, Andheri East, MUMBAI 400 093, INDIA. Tel. : 022-2683 6483 / 2683 1501 ...
www.vkpumps.com/contact.asp

---bmkhare

[sheiko]

Hi. I am asked by my senior to develop a process calculation spreadsheet to calculate positive pump hydraulic. I have a spreadsheet for calculating centrifugal hydraulic developed involving one suction and up to 3 discharge pathways. I think maybe I can modify the spreadsheet to suit for positive displacement pump. May any one help me in which variables I should modify or include in for Positive Displacement pump, like NPSH etc? As far as I know, positive displace pump deliver constant volume regardless the pressure. In the centrifugal pump, we have included the variables of capacity of the liquid to be pumped to discharge pathways. Can I assume that the flow rate of liquid from suction side will be the required pump capacity for positive displacement pump case?

I believe you only need to change "Heads" to "Pressures" in your calculation spreadsheet, for eg: change NPSH to NPIP (Net Positive Inlet Pressure).

However, in order to give you more precise advice, could you please upload the centrifugal pump spreadsheet?

Edited by sheiko, 22 May 2010 - 06:35 AM.

[sheiko]

I have attached a spreadsheet for PD pumps hydraulic calculations. Check it before using it.

Hope it helps.

Attached Files

•  PD- lg-stl jma.xls   423.5KB   641 downloads

[Erwin APRIANDI]

Dear zyy,

In principle all pump calculation are the same, since the pump did not develop pressure the pressure is develop by the system back pressure at the pump discharge. so the same spreadsheet that has been develop for centrifugal pump can also be use for positive displacement pump.

The positive displacement discharge flowrate can be control, but unlike the centrifugal pump. Discharge flow of the pump can not be control just by throttling a valve at upstream of the pump, but is should be control by variable speed motor.

I think it is better to understand further more regarding to the positive displacement pump working principle and performance curve before developing any spreadsheet on your on.

I also have seen the spreadshet given here, it's ok by me...

Hope it help

Attached Files

•  CONTROLLING POSITIVE DISPLACEMENT PUMPS.pdf   223.8KB   337 downloads