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View Full Version : How do you pump down the HPR?







Screwloose717
21-02-2012, 04:48 AM
Supervisor left me this "quiz" question. I can't figure it out. How do you get all the liquid out of the HPR and hopefully put it into a vacuum?

RANGER1
21-02-2012, 07:51 AM
Screwloose,
If its a simple system with no thermosyphon oil cooler etc, its easy.


Close inlet from condensors, then balance line.
As long as liquid reciever was not to full to begin with, low side of system will call for liquid out of reciever &
liquid will start to bank up in condensors.
If left long enough HPR will dbe the same as low side pressure.

There is a lot of ways to distribute the liquid from HPR if necassary, when it comes time to empty it.

Nh34life
28-02-2012, 06:45 AM
The best procedure is prep, i have seen many failed pump downs due to bad prep!
Ensure you know how much refrigerant volume you are dealing with and bring the LP and IP vessels down to a minimum setpoint (every system will be different) before transfer.
Shutdown the plant and isolate! shut liquid inlet and ballance as well as any other Peripheralconnections and force open/manually open LP or IP make up. If required dump any excess liquid to the field.
Have a pump out unit on standby incase you are unable to transfer all liquid in one foul swoop.
Have plenty of IBC's at the ready for venting to atmosphere if required (more than likely)
It easy easy spending the few extra hours in prep than having to deal with Ammonia vapour at partial pressure in you or a contractors face. (welders don't particually like fizzing steel will struggling to breathe)
I triple evacuate the line/vessel before allowing a cut in this 9 times out of ten ensures little to no ammonia vapour.
If there is not enough space in any evaporators or LP vessels you will need spare aux receivers or ammonia cylinders, this can usually be difficult to obtain if you don't already own one as ammonia suppliers arent usually willing to hand out vessels to be contaminated.

Screwloose717
19-03-2012, 02:41 PM
Ok, I'm a noob so you guys are going over my head. Close the condensor drain and the condensor/HPR equalizer line. Then dump liquid into surge drums for various freezers around the plant. Don't let that liquid into the evaporators, though. Keep a compressor(s) running. But won't the condensor fill up and liquid will want to run back down the discharge line?

Also, I would run a hose from the LPR to the HPR and get as much liquid into LPR as possible. But all our compressors use Liquid Injection cooling, so they would overheat and cut themselves off, not to mention the high head pressure because the NH3 in the condensor has nowhere to go.

Still confused.

sterl
19-03-2012, 05:09 PM
All of what you are saying is true; but every plant is different and has to be addressed differently. What you need is a containment volume that you can get to and maintain at a low enough pressure that is larger than the "preference" charge in the high pressure receiver. The preference charge is that volume in the HPR that will just maintain cooling for at least one compressor. Then you need to figure out how you are going to deliver the very last of the liquid out of the HPR to a lower pressure space.....Does the HPR have a low point connection or??
IIf this is a relative low temp plant and you have surge drums and big finned coils, the low pressure space is probably both the surge drums AND the coils....If they are in a small space so much the better. Providing the installed coils and drums represent enough volume: Cool the space way down, cut off the liquid makeup, wait, shut off the fans. This will leave you with the coil and surge drum close to empty and the space very cold. Shut off all evaps that are not part of the target for your remaining liquid. Valve off the Condenser Drains, Equalizing lines, any hot gas lines that head for your cold space. Run compressor and watch oil temp; condensers will fill up, HPR lievel will drop. Once compressor oil or discharge temp starts to rise: Close all valves associated with liquid injection and HPL line...; connect hose from Low Point on HPR to Liquid Feed to target Evaps. If the target space contains a large mass of product or ? at very low temp, start fans briefly to keep coil pressure low...

RANGER1
20-03-2012, 10:54 AM
Ok, I'm a noob so you guys are going over my head. Close the condensor drain and the condensor/HPR equalizer line. Then dump liquid into surge drums for various freezers around the plant. Don't let that liquid into the evaporators, though. Keep a compressor(s) running. But won't the condensor fill up and liquid will want to run back down the discharge line?

Also, I would run a hose from the LPR to the HPR and get as much liquid into LPR as possible. But all our compressors use Liquid Injection cooling, so they would overheat and cut themselves off, not to mention the high head pressure because the NH3 in the condensor has nowhere to go.

Still confused.


Condensers do not fill up in minutes on an average size system, so can handle a resonable amount of refrigerant.
You obviously don't have plant running 100%, you do it in a contrlled way & hopefully you won't even see discharge pressure increase at all.

Liquid injection (which you didn't originally mention) can be used until the level in liquid reciever is low, then transfer the rest to low side of system via drain valve on bottom of liquid reciever.

If a compressor is cool it can run for awhile part loaded before it cuts out, especially if set points of safeties on control panel don't limit things to much because on the liquid injection arrangements.
ie high discharge temp cut out 90 deg C
high oil temp cut out 60 deg C etc depending on oil type & compressor brand.

Nh34life
25-03-2012, 07:37 AM
You shouldnt require liquid injection while you are about to evacuate the HPR, just take it easy and run one machine at a time if poss whilst you set up.
The only way to learn this, is to do it or see it done...Safely!

Screwloose717
01-04-2012, 07:19 AM
Thanks to all who responded to this thread. We won't be doing any modifications to the HPR anytime soon. My supervisor just wants to get me thinking more like an engineer instead of a gauge checker/oil monkey. I'm new to the trade and I am glad I found this website. Refrigeration is an awesome trade and I hope to be doing it for the next 40 years or so. And even the day I retire, I bet I'll still learn something new.

Tycho
05-04-2012, 09:43 AM
1. run the low pressure receiver into vacuum
2. leave the system running
3. close the condenser drain and HPR equalizer line
4. run the compressors till you see the ice on the liquid injection pipe melting
5. close liquid injection valve and stop the compressors
6. Manually open the liquid injection/pilotvalve to dump the HP side into the LP side
7. leave the pilot valve open as long as the LPR is in a vacuum.

Depending on the pipe layout, you should be able to drain the HP side of liquid, and keep it in a vacuum.