3 replies to this topic

[Ghasem.Bashiri]

Dear Process Experts
Within a given process I need a pump that has 2-3 m3/hr Flowrate nad 2-3 Bar Head.
Originally we proposed Centrifuga type as default option but during checking with vendors they proposed Diaphragm type. As I checked with catalog of some famous vendors such pumps is available in centrifugal also but with 10-15% efficiency.
As this pump is small efficiency issue can be ignored from power side of view (total power of the pump is 0.4 kw). However I dont know exactly which one is suitable for me in this case: Centrifugal or Diaphragm.
Let me know your advise.
Fluid is hydrocarbon.
Someone told me that with centrifugal we have smooth flow and can control it with discharge valve.
But vendor of Diaphragm pump told me they can control flow in the pump from 0 to 100% design flow with stroke adjusment.
GB

[fallah]

Dear Process Experts
Within a given process I need a pump that has 2-3 m3/hr Flowrate nad 2-3 Bar Head.
Originally we proposed Centrifuga type as default option but during checking with vendors they proposed Diaphragm type. As I checked with catalog of some famous vendors such pumps is available in centrifugal also but with 10-15% efficiency.
As this pump is small efficiency issue can be ignored from power side of view (total power of the pump is 0.4 kw). However I dont know exactly which one is suitable for me in this case: Centrifugal or Diaphragm.
Let me know your advise.
Fluid is hydrocarbon.
Someone told me that with centrifugal we have smooth flow and can control it with discharge valve.
But vendor of Diaphragm pump told me they can control flow in the pump from 0 to 100% design flow with stroke adjusment.
GB

Ghasem,

Obviously, vendor is right about the possibility of flow control from 0 to 100% of design flow by stroke adjustment in PD pumps. With such low flow requirement and very low efficiency of centrifugal type, it is obvious that PD pump would be better choice for your application.

Fallah

[kkala]

In general a centrifugal pump has advantages, even though the specific application may affect pump selection. A centrifugal pump is not excluded for the data specified (about 11 gpm @ 30 ft). See Perry's "Chemical Engineers' handbook", 7th edition, McGraw-Hill 1997, Fig 10-26 (preliminary pump selection). Perry's diagram also indicates plunger pump, though it may not be a proper selection here (plunger pumps are for high heads, see http://en.wikipedia...ki/Plunger_pump).
A very similar subject has been discussed in the past, see http://www.cheresou...h__1#entry36154. Mentioned Perry's diagram is presented there by S.AHMAD (metric units).
Probably a centrifugal pump is preferrable over a diaphragm pump, if both types fit the application.
Note: Diaphragm pumps are said to have advantages in slurry transport, which is apparently not the case here.

Edited by kkala, 29 August 2011 - 10:17 AM.

[DB Shah]

Selection will depend on service & its criticallity. For such a small flow rate diaphragm pump will be preferable. It has no issue of dry running.

We have installed diaphragm pumps for such small service (Air operated pump). You just open the air valve and forget the pump for whole year.
If the service is not so critical you can explore such Air operated pump.
However consider following points-
- You will need to confirm your discharge pressure. Diaphragm pump discharge pressure will be limited by the motive fluid pressure (normally air or N2).
- There will be motive fluid loss which will be specified by vendor.
- Consider the scenario where the diaphragm leaks and motive fluid will travel with the process fluid. The concerns will be explosive mixture (if you use air), if the discharge is to a atmospheric storage tank you will need to consider the amount of leak air or N2 ingress to calculate the SV capacity of the tank.