ammonia pump problem

[Sukhvinder]

can anyone help me about ammonia recirculation pump?

we are using ammonia over feed system in our cold storage, when we run the compressor the pump get down! without compressor the ammonia runs at 7 kgs without any problem but when we run the compressor the pump get down.

please help me out!

[mimo]

Sir,
maybe you are using a small capacity NH3 pump. Better replace it with a bigger capacity..

[sterl]

What changed? Pump? Liquid Level? Count of Evaps? Thsi pump spinning but not making pressure or cutting off due to a control/electrical/lqiudi level issue? What is make and model of pump and how the liquid level in the vessel controlled and measured? Can you make some sketch of how the delivery from the vessel to the pump is piped? Details count....

With compressor running: refrigerant in the vessel is being cooled by its own evaporation....Makes bubbles.
Pump inlet flow can simply pick up the bubbles and you will have little pressure pulsations and some rattling at the pump impellor...so the velocity down the suction leg has to be low enough that the bubbles rise and don't get sucked down by the moving liquid....so your vessel and its liquid level and the piping between have to be large enough and high enough need to both prevent and deal with the bubbles....BUT:

Refrigerant in pump and immediately upstream of pump can then do a number of different things: if there is a vapor pocket trapped within a non-operating pump, it will grow as the pressure reduces; and the pump may not be able to clear it. Really bad piping will introduce the "pocket" of the non-operating pump, to the suction of the operating pump. Same sort of thing can happen in the immediate upstream piping even under flow.... Large high point in that portion of pipe tends to accumulate vapor; and soomer or later pocket of vapor grows and gets pushed into pump housing. Big jerk, sometimes, but can also completely stop flow.

Depending on nature of the pump: It can swirl the incoming flow which develops a vortex where the suction pipe enters the vessel (like flushing a toilet) and there will be a "tube" of vapor all the way to the pump inlet; add that to the "wrong" inlet piping geometry and you will collect vapor in a portion of suction pipe such that it can't rise back to the vessel; eventually it grows and seals the pump's suction cavity from the vessel liquid and the pump drinks the "void" and all flow stops....

Conventional cavitation occurs when the liquid moves very fast with respect to the blades of the impellor; so fast that cavities of vapor are left on the backside of every impellor vane...the vapor travels toward the discharge of the pump and the higher local pressure causes the cavity to collapse: iitsounds like gravel is going through the pump, in most case. And its very rough on seals, bearings, impellor surfaces and so on.

Mostly: this type can be cleared by stopping the pump; close the discharge down to a very small opening; start the pump; open discharge very slowly. If the pump discharge pressure does not twitch: it should start high and decrease as you permit the pump flow to increase. If you are asking for too much flow from the pump: the discharge pressure will start to surge and swing and twitch before the discharge valve is all the way open.

Describe for us what's gone on to change any of these characteristics and maybe we can help...But maybe not, too.

[lowtempman]

good analysis, Sterl...you could be an old fart like me..........maybe we know each other.

[get the gauges]

Thanks for that little lesson.

[Magoo]

Rapid pull down will create cavitation at the pump infeed. So slow down the compressor loading rates. Soft and easy slow and controlled.
The pump should be at least 2 metres below the accumulator with anti cavitaion plate in place. Plus votex plate before pump inlet.

[srinivasan_m47@]

I am in india .Pl call me 09335921043