Requirement of Throttling for Chemical Injection lines besides Pump Stroke Adjustment

[Sawsan311]

Dear All,

I would like to enquire whether from operational perspective, there is a need to have throttling at the chemical injection point besides knowing that the chemical dosage can be adjusted via the pump stroke. The example I am presenting here is only for a single injection point fed from its dedicated diaphragm pump i.e. no sharing of multiple injection points from the same head.

Thanks

Regards,

 

[pierreick]

Hi ,
The answer is NO ! You adjust the flow with the stroke. Refer to operation manual from vendor and perform a safety hazard analysis to understand the risk associated with a valve at the discharge of the pump .
Good luck
Pierre

 

[LittleInch]

You need to understand the difference between positive displacement pumps like this and centrifugal pumps.

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

 

[Sawsan311]

Hi littleneck, I am clearly talking about chemical injection application which have positive displacement pumps.

Thanks Pierreick, I was wondering why some operation personnel prefer having needle valves near the injection point to tune the dosage, I understand that this can surely lead to frequent operation of the chemical pump in recycle PRV path (if available) or popping of the discharge PSV in case valve is forgotten closed.

 

[LittleInch]

Sawsan, that's my point - you need to educate the operators that a control valve on a PD pump is incorrect and they need to adjust the pump stroke or the pump rpm if they want to vary flow. Restricting flow on a PD pump as you say operates relief valves which then don't re-seat properly and is not the way it is supposed to work. Either remove them or wind them fully open and lock them open.

Operations personnel tend not to have knowledge of such things and they see a control valve in other applications where there are centrifugal pumps or a supply line with pressure and assume all systems are the same.

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

 

[Latexman]

Operationally, there is no need or benefit. At best (BP < MAWP), it requires the PD pump to work harder and consume more energy to do the same function (less efficient). At worst (BP >= MAWP), one has created a scenario that activates the PD pumps relief system unnecessarily. No good will come of this. As such, the enquiry demonstrates a lack of understanding of basic PD pump technology and knowledge.

One does not close a line valve on a running PD pump, which is a constant volumetric flow rate machine. That's rule #1 in PD Pump 101.

Good Luck,
Latexman

 

[Sawsan311]

Great, Thanks All, I was in the first place negating such ''tuning chemical valves'' requested by OPS and your feedback confirmed that no such accessories require to be put in place.

regards,