Diaphragm metering pump suction pressure

[amar122amar]

We have a metering (diaphragm) type pump with design suction pressure 4.5 barg, discharge pressure 42 barg, flow rate 8 LPM. What may be the possible adverse effects on pump, its performance if suction pressure goes abnormally high for eg. say 40 barg?

 

[BigInch]

You'll obviously overpressure all of the pump and discharge piping.
Check the pump's pressure rating.

 

[moltenmetal]

You might be able to over-pressure the downstream piping, or you might not. Your suction piping is presumed capable of handling this high pressure- if not, it will be damaged whether the pump is running or not.

If the suction pressure rises to 40 bar and the discharge pressure is relieved back to the suction, you are not protected if the suction pressure rises. You need the relief valve to discharge elsewhere. And yes, you should have relief on the discharge PIPING of any PD pump which is capable of a pressure at dead-head which can damage the piping or downstream equipment.

If it is a hydraulic diaphragm pump, the internal hydraulic relief that such pumps usually have, is referenced to atmosphere rather than to suction pressure. If it is set properly, once the hydraulic relief pressure is reached, the pump will simply stop pumping hydraulic oil to the diaphragm and the diaphragm will cease to move. However, you should NOT rely on that internal hydraulic relief to protect anything other than the pump itself.

The pump itself is unlikely to be damaged, but that depends on design and you need to verify that with the manufacturer.

 

[amar122amar]

Thanks for ur comments. The suction piping is rated for 40 barg so it is protected for high pressure. So what I understand from ur comments is that if Philip's internal relief valve pops then it will stop working but there won't be any physical damage on pump.

 

[amar122amar]

Correction *pump's not Philip's

 

[moltenmetal]

You need to verify that with the manufacturer of your pump, but most hydraulic diaphragm pumps do work that way.

 

[amar122amar]

Ok thanks

 

[micalbrch]

What (medium side) check valves are installed? Ball valves? The high suction pressure can have a negative effect upon the accuracy as the suction valves may open too early and Close too late due to the high suction pressure. And - but that is difficult to say without knowing the exact design and model of the pump - the diaphragm is no longer "pressure balanced" during a suction stroke. The hydraulic piston usually draws the diaphragm backwards during a suction stroke but with such a high suction pressure the diaphragm will be rapdily pushed backwards before the piston has performed ist entire suction stroke.

Last but not least you must check with the manufacturer if there is any negative effect for the gear. Will it get sufficient lubrication for all parts during an entire revolution?

 

[LittleInch]

With such a low differential pressure, the metering accuracy cold very easily suffer by a few percent and if your discharge pressure drops even a small amount, direct flow through has an increased potential or simply that the NRVs won't work correctly and you end up pump back and forth with no real forward flow.

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

 

[bimr]

It would depend on what type of metering pump is in use

 

[amar122amar]

It is Leva adjustable stroke diaphragm pump. Thanks for comments.

 

[amar122amar]

Thanks moltenmetal (Chemical)for valuable comments

 

[bimr]

Should work as long as the pump is in serviceable condition and the pump specifications are met.

Some of the Lewa pumps are good to 400 bar suction pressure.

 

[georgeverghese]

Whilst there are concerns with the capacity of an internal RV that goes back to pump suction with variable pressure, standard industry process safety practice is not to rely on this internal vendor supplied RV for the overpressure protection of the downstream system - this should be addressed with a regularly maintained and calibrated PSV sitting on the discharge piping. The type of PSV and the backpressure correction factor used in the sizing of this PSV should suit the max normal built up backpressure seen on the RV discharge at relieving conditions. If the backpressure is too high for any type of code designed RV, then limiting measures will have to be implemented.

 

[amar122amar]

Yes Georgeverghese. Thanks for comments.