Positive suction or flooded suction required for dosing pump ( bottom suct, top discharge)

[bmw318be]

Hi,

Understand that the metering dosing pump,api 675 has bottom suction and top discharge, the pumping principle is using plunger and diapraghm to create suction and the hydraulic oil push the diapraghm extend and retrext to create suction and discharge of precise amount of liquid.


My question is:

In order to logically be able to pump to the maximum, how we can calculate or doing an experiment to determine the minimum suction head required.


Is there a practical way yet simple to use any vacuum gauge at the suction to determine the minimum suction pressure required.

We see from the testing that dosing diaphraghm pump is having a very good suction capabilities, however the manufacturer always says must operate at positive suction bilud did not elaborate how much minimum.

1. What does positive suction referring ? , how exactly we have to have good suction head level, in most cases, it is suction lift condition.

2. Can the condition be a suction lift condition with the NPHSHa would still.be positive ? ,

3. My understanding suction lift is negative suction and correct me if i am not correct, npsh a is zero here. No pressure to push the liquid to the sucttion of the pump.


4. If you have any dosing pump installation, please share that posotive suction, would the liquid has to be at least reach the diapraghm of the pump


5. I know some of you are probably understand that most start up case when we open up the tank water supply, and shall minimum we see the suction gauge at the suction shall not be negative and the water shall go through to the pump head or diapraghm and even better going through the discharge, then we conclude that the sysytem is having sufficient positive suction ? . I am not sure if dosing pump we shall expect this as inside the diapraghm there is seat valves at suction and discharge with ball valves, foes this sufficient positive suction applies to this dosing

 

[Compositepro]

npsh is measured in units of absolute pressure, not gage pressure. So npsh can never be negative. This should answer your question. If you do not understand the difference between absolute and gage pressure, do a Google search.

 

[LittleInch]

As NPSH is always positive, in answer to your question 1, without seeing the vendor info it is difficult to say, but would appear to mean above atmospheric pressure to me.

Metering pumps needs to be filled reliably to pump accurately, whereas normal diaphragm pumps are less particular.

Yes npsh would still be positive in a lift condition

The pressure pushing the liquid is atmospheric pressure assuming you have a tank open to atmosphere.

If you have discharge pressure our connecting pressure less than inlet pressure for this sort of pump you can get free flow through the pump and it won't meter properly.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[itdepends]

Positive in this instance means above atmospheric pressure inside the pump. Operating below that is possible if you get all the air out of the pump during initial priming- but if you have a leak in the suction line or air starts to accumulate/degas inside the pump it can accumulate and reduce the pump performance significantly.



As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"