Chiller Pumps - Leaking Seals

[mrice1671]

Hi,

I have a 120 Ton multistack chiller with two armstrong series 4382 25HP Pumps with 6" inlet and a 6" outlet that immediately gets reduced to a 4" header in the chiller. We have three of these chillers on-site and have found the seals leaking on all the primary pumps of each chiller. (secondary pumps are only for backup). We originally had to up-size the pump from a 15HP to a 25HP and we're getting about 430gpm. We've already replaced one seal on a pump and the new seal started leaking a few weeks down the road. The seals we have are spec'd for these pumps and are meant for systems with over 30% glycol. We have 35% in our system. We originally had a lot of air in the system that we thought could potentially heat up when cavitating in the pump and ruining the seals. We now have air separators on the chilled water system so it shouldn't be the problem.

Any ideas?

 

[JJPellin]

We have found that ethylene glycol can be very difficult to seal. We have had chronic leaks on many of our glycol pumps and have largely been unsuccessful in getting them to stop. At least one of the issues is the type of glycol used. If the system uses automotive anti-freeze, the additives can be a problem. Even in the commercials, they brag about how their additives coat all metal surfaces to resist corrosion. Those same additives plate out on the seal faces and cause the seal to drip. For systems that use industrial ethylene glycol and not automotive anti-freeze, there are different grades with different additive packages that can be better or worse on mechanical seals. We are working with our lubricant supplier to convert some of our systems over to a different product that is supposed to have fewer issues with mechanical seals. In other systems, we have given up all hope. We are converting some of these systems to seal-less pumps (either mag drive or canned motor).

Johnny Pellin

 

[mrice1671]

We have propylene glycol in our chilled water system which I've read is more leaky than ethylene due to ethylene having a higher surface tension. We've had some questioning on the 6" inlet of the pump dumping into a 4" header and causing a high differential pressure. However, Armstrong says their pumps are rated for the differential pressure and our chiller rep (Multistack) says that it's not a problem. Another concern is that the chiller pumps are not on VFD's which would give the pumps a soft start rather than our setup with an immediate 0-100% start. I've uploaded a picture of the seal that was busted. You can see that the seal somehow cracked.

This tells me it's not just leaky, the seal came in a brand new pump and was only worked for a couple months.

And feedback?
-Mike

 

[georgeverghese]

How does air get into this coolant circuit ? Though you have air seps now, does this mean your EG-water coolant is air saturated ? - that could lead to corrosion due to EG decomposition. The elastomer component on these seals should be upgraded to withstand acidic conditions otherwise - what do you have now ?- nitrile rubber or similar? Why cant your seal supplier give you some thing better?

An automated startup bypass around the chiller pump may help to reduce startup stresses as an alternate to VFD?

The seal may also be failing because of air lock up in the seal chamber ( the air sep may not be 100% efficient) - that could lead to loss of seal cooling. See if you can stop this air getting into the coolant circuit. On the other hand, the feed inlet and exit nozzle arrangement on the upstream coolant expansion drum may not be permitting the coolant to degas properly.

 

[keyepitts]

Several things here; looking at the picture, the elastomer (Viton?) has melted, so the seal has gotten very hot, most likely by dry running, could however also be caused by the rotating and stationary faces seizing (silicon carbide/silicon carbide ?). The cracking of the face probably happened after the elastomer melted and allowed the face to move and contact the shaft. This seal would have had a massive leak rate if operated in this condition. A double seal arrangement with a pressurized seal chamber (plan 53A or 54 maybe)would likely solve your issues. Another solution would be a seal-less mag drive pump.

 

[Chpal1984]

You should be ok using Viton with such a process. What are your operating temperature and pressures?

There are a number of things that could be leading to your seal dry running. Whats the elastomer material? How quickly does your speed ramp up? (i.e. 0 to 3600 rpm is 30 seconds) Is there a flush plan? any piping plan already with it? Does your process require you to vent on startup?