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jessica
24-04-2007, 02:29 AM
Dear all,

Regarding the liquid overfeed system (ammonia), 3 ammonia liquid pump (2 used 1 standby) can be installed in parallel. Its performance is good. Is that possible to install 4 ammonia liquid pump (3 used 1 standby)? What is the factor that should i consider?

Thanks a lot

US Iceman
24-04-2007, 03:40 AM
If the refrigerant pumps are the centrifugal type I would not recommend running more than 1 pump (never in parallel).

The reason for this is the pumps fight one another due to discharge pressure changes. One pump will run higher pressure than the other adjacent pump. This causes the pumps to change operation on the pump curves. So, one pump will pump more volume at a lower discharge pressure than the other pump.

Theory says you can run centrifugal pumps in parallel, but in practice it does not work very well.

If you need more flow, then use a larger single pump is my advice.

Multiple pumps in parallel are extremely difficult to commission properly.:(

NH3LVR
24-04-2007, 04:22 AM
I have never tried running NH3 pumps in parallel, but you have me curious. I will check the Cornell Pump website and see what they have online.
http://www.cornellpump.com/

I have run identical pumps (H20) in parallel with success. They see the same discharge pressure, the discharge line. I do realize that they are differences between identical pumps, but it has worked for me.

What will NOT work is to use a VFD and attempt to trim one pump to control the output of multiple pumps. The check valve on the VFD pump does not open until it comes up to discharge pressure. You have almost no control. We defeated that problem by running two pumps off of one VFD.

US Iceman
24-04-2007, 04:42 AM
I have seen many installations with pumps in parallel and you can "make them" work. I had a long discussion with Cornell about this last year. The gentleman said basically... everyone tries this with limited degrees of success.

The biggest problem I can see is where you have NPSH problems and cavitation. If a pump is operating under a low head condition, the pump flow goes up as does the NPSH required.

I think what ends up making this a somewhat livable situation is the excess refrigerant we pumping and that almost invariably the pumps are over-sized for head and flow.

It is a similar problem to not having the hand expansion valves closed enough for liquid balancing to the evaporators.

NH3LVR
24-04-2007, 02:45 PM
I had a long discussion with Cornell about this last year. The gentleman said basically... everyone tries this with limited degrees of success.
As usual Iceman, you were a step ahead of me.:(

US Iceman
24-04-2007, 02:48 PM
Perhaps

It helps to have some good people on here to keep you on your toes too.;)

Tycho
24-04-2007, 09:40 PM
You guys are obviously using the wrong pump :D

Here's what you should be looking at

http://www.pbase.com/kimmo98/image/77698101.jpg

Andy
24-04-2007, 11:27 PM
You guys are obviously using the wrong pump :D

Here's what you should be looking at

http://www.pbase.com/kimmo98/image/77698101.jpg


Tyco,
what pray tell is that beast.

Parrallel pumps do work, but require each to have it's own drop leg.
Me I would fit one pump and a standby, but what do I know;)

Kind Regards Andy:)

Tycho
25-04-2007, 11:49 PM
Tyco,
what pray tell is that beast.

Parrallel pumps do work, but require each to have it's own drop leg.
Me I would fit one pump and a standby, but what do I know;)

Kind Regards Andy:)


It's the Kvśrner centrifugal pump, been produced for over 40 years with little to non design change, can be fitted with both electric, and hydraulig motors (for use on gas tankers or similar places)

requires a minimum suction head of 1 meter, runs dry and chews gravel with no problems :)

The outlet port can be rotated 360 degrees (every 45 degree).

Only downside I can think of is that it weighs 90 Kg not including the motor, and is a "female dog" handle if you are alone. carrying the new one down two decks works ok, but by the time you have the old one out and on the deck and the new one in place, you need help to carry the old one up...

Thrust bearings in the center, roller bearing on top, two mechanical seals. as long as you mind the oil level it'll run till the cows come home.

we run a "exchange system" with them, if you have a break down, we send you a new one, you return the old one and we charge for a overhaul (think it's $1200, hours and spareparts). all bearings seals and o-rings are changed so it's as close to a new pump as it gets.

one of the guys who designed it has one running a fountain in his garden :)

Sergei
27-04-2007, 05:51 PM
A while ago I worked on gas carrier. We had common discharge for 6 pumps. They worked fine. Certainly, real capacity of each pump was not equal. Some pumps had capacities 10-20% more than others. We had Kvaerner pumps. So no problem on discharge side. I agree with Andy that suction side should be design properly(separate drop leg for each pump).

Ponca Dave
16-02-2008, 10:27 AM
Dear all,

Regarding the liquid overfeed system (ammonia), 3 ammonia liquid pump (2 used 1 standby) can be installed in parallel. Its performance is good. Is that possible to install 4 ammonia liquid pump (3 used 1 standby)? What is the factor that should i consider?

Thanks a lot
I've never used more than 2 w/ 1 standby. Size them right.Why complicate the complicated.Calculate to 4:1 and there should be no problem.

ntfreezer
20-02-2008, 09:23 AM
I think the hermitic pump is the best in quality. I have used a lot of hermitic pumps in ammonia system. I have met a problem.

Plank!
20-02-2008, 11:49 PM
I think the hermitic pump is the best in quality. I have used a lot of hermitic pumps in ammonia system. I have met a problem.

You've been lucky then ;)
A company i worked for 5 or 6 years ago had a run of bad luck with hermetic's.
From the debris i found in the pumps i'm guessing that the pipe fitters did not do a good job of cleaning grinding dust out of the pipework before welding.
Destroyed the liquid seal (anti recirculation) on the inlet end of the impellor, and the same on the mating surface of the inlet casting.
The pumps were a write off, never managed to get decent pressure/flow from them again.:(

Inlet strainers are your pumps friend:)

US Iceman
21-02-2008, 02:39 AM
Inlet strainers are your pumps friend:)


I might question this. When the strainers get dirty the pressure drop across them could cause the refrigerant to flash off resulting in pump cavitation.

NH3LVR
21-02-2008, 03:08 AM
Inlet strainers are your pumps friend:)

I would be afraid to apply an inlet strainer on an NH3 pump. Oil at low temps could cause severe cavitation and be almost impossible to remove.

TXiceman
21-02-2008, 03:32 AM
I would be afraid to apply an inlet strainer on an NH3 pump. Oil at low temps could cause severe cavitation and be almost impossible to remove.

I have to agree here. Maybe a start up sock for a week or so on a new installation.


Hansen and Teikoku, both work well if installed properly. Most of the problem pumps I have seen have been problem designs.

Ken

Plank!
21-02-2008, 03:34 AM
On reflection the idea of strainers before the pump is a bit daft. Certainly i don't remember seeing any on any of our projects.
The debris probably got there during a pipe modification to reduce oil logging in the standby pumps (4 pumps 1 - 3 running depending on cooler/blast duty) three of them were destroyed by the abrasives left in the pipework.

US Iceman
21-02-2008, 08:00 PM
Dirty systems could be considered to be a enemy to hermetic pumps because of the pumps carbon bearings.

sreenivasarao
08-03-2008, 08:24 PM
You guys are obviously using the wrong pump :D

Here's what you should be looking at


hello dear i am sreenu from india canu u help me we riquied ammoina liquied pump for 60 tr at -25 c temp what type of ammoin pump requed hp also tell me and pump supplayers adders tell me thank u

mazbut
30-05-2008, 12:53 PM
A positive displacement Douglas pumps is the answer. I had also been using Mohno pumps effectively for pumping Ammonia liquid,,,,

Once I couldnt find a liquid pumps so what I could do was to install a mono-block centrifugal water pump to do the j0b for the time being,,,unfortunately it didnt work for long and soon leaked from the seals !

for good sealing you should choose a positive dispacement pumps or even a centrifugal pumps with double seat and longer gland box to ensure proper sealing