View Full Version : Faulty Lederle Hermetic Ammonia Pump.

21-09-2016, 06:53 PM
Hi Guys.
I have a LT Surge Drum with 2 CNF 40 Liquid Ammonia Pumps.

Both Pumps have identical valves and pipework with "Hermetic CFR regulators" after the pumps.

These from the little I have learnt so far regulate the flow of liquid from the pump??

According to the site PID they also are a non return valve.
Which makes sense, however pump 1 when at rest shows the pump suction and discharge pressures in equilibrium (Both the same!).

Pump 1 runs fine. Displaying Pump pressure of approx. 1.98 Bar.

Pump 2 pulls high Amps and eventually trips on the Low pump diff switch. Also it's measured Pump pressure displays approx. 1.46 Bar.

When referring to the manual I have it suggests that the pump might be running on 2 phases!

I will check that tomorrow when I am scheduled to return to investigate the pump issues.
I am pretty sure I have actually checked this before and found no issue!
But Hey I will check it again tomorrow.

Anyone got any ideas?
Thanks Grizzly

21-09-2016, 09:29 PM
Hello Grizzly,
dirt, oil, flow orifice.

21-09-2016, 10:33 PM
As you say check phases first.
High amps could mean bearings worn & rotor contacting "can" or pump full of cold oil.
Hopefully oil.
Is this the flow valve you are referring too?
This one does not have inbuilt check, but only one I know of.
See troubleshooting in second link.



22-09-2016, 07:25 AM
Hi Guys.
Thanks for your input.
I will be back later with some more info / answers.
Need to get going!
Busy day ahead.

22-09-2016, 08:17 AM
Hi Grizzly,
I agree all previous comments, if you can run both pumps together, check drawn amps, they should be the same per pump. If one still has high amps, I agree with ranger that the carbon bearings out of spec' and rotor is dragging on rotor sleeve. And will break through into winding and kill the pump, so strip it out and repair. There will be a max flow orfice disc in the discharge flange, the vessel should have anti cavitation plates inside vessel.
Have fun ..... magoo

22-09-2016, 06:46 PM
Hi Grizzly
using a CFR flow regulator, there is no max flow orifice disc. if for any reason the CFR doesn't operate properly, the pump can operate at overflow.
check for both pump pressure in discharge line after the regulator, there should be more pressure in line with the faulty pump.

22-09-2016, 10:38 PM
Hi Guys.
Long Day Not so short answer!
Not shown on the schematic.
But just after the CFR you see two teed lines going off to the right and shooting up the page vertically.
These are Pump minimum pressure bypass lines with isolation valves at the top of the Surge Drum.
Guess which one was cracked open and which one was fully open?
The Bypass / vent line according to the drawing also has a orifice in it.

I forgot to say the No1 pump is as you would expect covered in Ice.
Whereas no 2 was without Ice.

After a long day of proving voltages, Amps being Drawn, proving no thick oil present etc.
Using a hot air gun proved that there was little or no Liquid at the pump.
Nothing made sense!
A Vapour Lock?
The liquid and Discharge valves were shut and whilst attempting to shut the Balance / vent line it was found to be almost shut. Closed fully anyway.
Using the liquid pump suction gauge line complete with service valve off the top of the pump. The pump was vented off.
No Liquid just vapour!!!
With Pump and pipework Purged, purge line shut Diff. Gauge line reconnected.
Main surge drum / suction line Valve opened and Pump and surrounding pipes cooled rapidly.
Sticky finger indicating liquid present.
Remaining 2 valves opened fully.
Pump Ran and a small pump diff indicated, where previously none was shown.
The Pump Pressure was now 1.6bar and stable with around 6 Amps being drawn. Pump was left running and cooler temps within the cold store monitored.
After about an 1.5 hrs. running the pump pressure suddenly shot up to 1.9 to 2 bar. with no increase in running amps.

Summary is.
Pump no 2 was turned off and no1 ran to balance the pump run Hrs. After many Months no 2 was turned on to again rotate the running hours.
Whilst it had been off the pump and the liquid ammonia inside had warmed up. The internal pressure became greater than the surge drum / suction line pressure.

But not greater than discharge pressure on the far side of the Non return valve (after the CFR Valve).
(Sticking valve or valves to be considered also!)
With this Back pressure when the pump was ran it was starved of liquid and the amps would shoot up.

With the pressures re-balanced the pump ran but with reduced pump pressure.

Something was initially still restricting pump flow.
So I intend to obtain a spare Lederle Hermetic CFR Valve and a new non return valve.
Because the pump pressure diff being so small, leads me to suspect one or the other was/ is malfunctioning.

Anyways a good interesting day at the end of it.

Cheers Grizzly