Discharge flow and pressure 2

[Pumpmeup]

Hi, have a question regarding a CR 3-33 A-FGJ-A-E-HQQE
Vertical, multistage centrifugal pump with inlet and outlet ports on same the level (inline).

The pump is rated to 3kl/h with a max pressure of 2500kpa.

Currently running as a glandwater pump for a Single warman slurry pump with Maric restricter of 19 litres/hr.

What I wanted to know is could we run a second pumps glandwater off the same pump with minimal pressure loss... as the second pump also has a Maric restrictor on or would the addition of the extra flow drop the discharge pressure? ... need minimum 2000kpa out of both discharges

 

[TugboatEng]

Pump curves, please.

 

[Pumpmeup]

https://product-selection.grundfos....tid=GMA&productnumber=96513351&qcid=926239685

 

[LittleInch]

Can you double check those numbers please?

From what you've said you have a pump with a duty point of 3,000 litres/hour but your only flow is 19 litres/hour??

You therefore appear to be running the pump essentially as a dead head unit well below what looks like the pump vendors minimum flow of about 1200 litres/hr ( where the lines go thick)

UInless you have some sort of minimum bypass arrangement which you haven't told us about this pump won't last very long.

Also where is the pressure requirement relative to the pump flange in elevation?

And what is your inlet pressure?

If you're getting 25 bar out of this you must be getting a decent inlet pressure as the max differential form the pump looks to be about 22 bar at dead head.

If your flow units are correct then you could hang about 100 pumps off this one without reducing the discharge pressure below 20 bar.

BTW I looked up the Maric restrictor - never seen them before but will remember them now.

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

 

[Pumpmeup]

Sorry was meant to be 19 litres/minute through the Maric. Pump draws straight off a tank.. and discharged to only 1m above the pump and only 10m away.

 

[Artisi]

LI, the maric style restricter are usually found in hotels etc, to control flowrate thru' the showers and hand basin taps, have also see them used in HVAC and in gland water control as used here. A very handy device.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Artisi]

Pumpmeup,
No problem running a second system.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

OK, that's better.

So flow now is 1.14m3/hr which puts you on 210m head differential head and just on the edge of the minimum continuous flow of the pump.

If you have say 5m liquid head in your tank and ignoring frictional losses, that a discharge pressure of about 21.5bar or 2150 kPA, not your 2500 quoted??

Another pump wanting the same flow is now a total of 2.3 m3/hr so you're at about 190m. with the extra 5m (say) you're now looking at a discharge pressure of about 19.3 bar or 1930 kPa.

So high tight is your requirement for 2000kPa?

Also can you accurately measure what your discharge pressure is now or advise what is the liquid level in your tank above the pump inlet level?

Pump curves for this sort of unit can be +/- 10% so you need to calibrate what your ACTUAL pump is giving you.

And yes that maric restrictor looks great - can't believe I've not come across it before. Is it a Aussie / Far east thing?

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

 

[Pumpmeup]

Ok so the tank the pump draws from only has approx 1.5m of liquid head in it... am I right in saying that the higher the suction pressure the higher the Discharge pressure will be? So if we decided to change the suction of the pump so that it draws off a pressurised line of line of say 800kpa? that would keep the discharge pressure above that required 2000kpa?

Yes we have pressure gauges on discharge line of pump.. so can measure.

 

[TugboatEng]

What is the importance of the discharge pressure? If the system is a closed loop and you're trying to force a flow through an orifice or nozzle and you increase the pressure on the exhaust side of said nozzle or orifice then you will defeat any gains in discharge pressure at the pump.

 

[Pumpmeup]

It’s not a closed loop... it discharges into the stuffing box of a slurry for pump at a rate of 19 litres/minute

 

[Pumpmeup]

Importance is that the glandwater pressure needs to be 200kpa higher than the slurry pump it is feeding the packing of pressure

 

[LittleInch]

In short yes you're correct. Inlet pressure + differential head from your pump curve = discharge pressure.

However be careful. The may be a low limit on allowable inlet pressure and a limit on maximum discharge pressure. Look at your pump details or ask the vendor.

Also do some tests yourself on the pump. Many small pumps are never tested individually so you may not need to boost the inlet pressure. If you can measure flow and divert some extra flow you can generate your actual pump curve.

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