Hi all,
Thanks to everybody that responded. Unfortunately, I didn't get enough
information to estimate the lifetime of the helium compressors. I got
several responses from people who wanted to know the same thing I did, but
not many from people who had information.
My general feeling now is that the compressors can be expected to last
3-5 years without breaking down. You can increase the likelihood of it
being five years by taking good care of them. The main ways to do that is
to make sure that they are adequately cooled, and to make sure the the
helium is very pure. Running them hot or with impure helium will cause
them to break down faster.
One person recommended carefully monitering the water flow and
temperature, and frequently backflushing with an acidic cleanser to remove
buildup. I talked to one of the Bruker cryoservice engineers and he told
me that while this might be a good idea in principle, that he didn't
recommend doing it. He thought there was at least a chance that you could
eat through the walls of the copper pipe in the heat exchanger in the
compressor and cause water to leak into the helium, which could
potentially damage the whole system. Also, if Bruker or Sumitomo found out
you had done this it would void any warranties and make Bruker generally
less inclined to help you out with your cryoplatform problems (ie sending
engineers out without charging you).
We also measured the water flow through the compressor and although the
compressor is running about 5 deg C too hot, the water flow was actually
too high. Sumitomo gives a spec in the form of a graph and it actually
shows an upper limit to the water flow. The Bruker engineer thought that
if the water flow was too high, the heat transfer would actually be
reduced. So he recommended that I install a bypass to remove some of the
flow from the compressor. He thinks that this will actually cool the
compressor better. I'm not entirely convinced, but I'm going to try it.
I'm also going to install filters and a flow meter. Then I'll be able to
monitor the flow carefully and at least backflush the compressor and/or
change the water pump when the flow gets low. I'm not going to use the
acidic cleanser.
Here are the responses I got, minus identifying information. My original
post is at the bottom:
**************************************************************************
I will be eager to look at the numbers you post later. We had one
cryoprobe installed six months ago and functioning fine but we were not
lucky with the other one. We got a kind of lemon piece, I suppose.
Essentially, when we put the compressor on a platform and hooked up
everything and the engineer started installation, he found this humongous
He gas leak and everything ground to a halt.
Now we have shipped the compressor for repairs and keeping the fingers
crossed.
**************************************************************************
Have you looked into why the capsules are having repeated failures?
Perhaps there is a problem with your cooling, electrical service, or your
helium supply.
Our compressor kept overheating because the heat exchanger became clogged
with lime and bacteria. Now we backflush the heat exchanger whenever the
cooling water output temperature rises above normal. Air-cooled units can
have the same sort of problems if flow is restricted by dirt. Service
life of a compressor is inversely proportional to the average operating
temperature. If you run the compressor near it's high temperature limits,
you should only expect it to last barely through the warranty.
For most equipment maximum current draw is normally only for a second at
startup. Then the load drops off after capacitors charge, motors start,
etc. Coldhead compressors are just the opposite. They start easily, but
the load increases steadily to maximum, where they run all of the time.
For this reason, the electrical service must be designed with some excess
capacity in order to prevent the compressor running on low voltage due to
electrical equipment heating at constant max. load.
The compressor motor runs on 3-phase power. All 3-phase motors are
sensitive to phase voltage balance. If your power has poor balance (the
voltage of the 3 legs are not equal) then the compressor service life will
be shortened.
Impurities in the helium gas supply will also decrease the service life.
If the cylinder is changed without purging the regulator, or if you use
less than Grade 6 gas, expect a shorter service life. When one replaces
the compressor capsule, it is nearly impossible to remove all of the
impurities introduced during the repair. For that reason, you should
never expect a repaired compressor to last as long as a new one.
With proper service and operating conditions, your compressors should last
at least 5 years, IMHO.
-------------------------------------------------------------------------
(and from the same person):
5 years is just my professional estimate. IMHO is "in my humble opinion."
To backflush you need an acidic cleaner, which you can buy from an
industrial supply house. Reversing flow only gives a mechanical assist to
the cleaner. Our A/C shop has a solution made up for flushing all of the
air handlers, and I 'borrow' some of theirs whenever I backflush. You
could put in a 4-valve crossover to reverse flow. You would just need to
fill your neslab with the acid cleaner, which would clean both heat
exchangers except the city water side of the neslab. Be careful not to
eat away the copper heat exchanger with too strong an acid.
Here, I just run the campus cooling water through the compressor. With a
neslab, you're just adding another layer of mechanical problems, as you
indicate. I have a bank of filters to take out the muck, and some valving
to allow me to change one bank of filters at a time while leaving the
compressor running. To backflush, I have to stop the compressor and plumb
in a garden pump to circulate the acid. One more round of engineering
changes, and I'll have the valves set up to connect the pump without
stopping the compressor.
An infrared thermometer is very handy for measuring the temperatures, and
I have a flow meter plumbed in series with the compressor.
***************************************************************************
We have two cryoprobes. One, installed exactly six years ago this
week, has given no problems at all with regard to the compressor except
for the adsorber replacement (part of the annual service).
The other was installed just over a year ago and likewise the compressor
has given no problems except to replace a fuse in the coldhead drive
circuit once.
***************************************************************************
We have a TCI-cryoprobe on our AV700. It is only about 18months old,
and has been performing very well. I will certainly keep an eye on
things as we approach the 3 year anniversary.
***************************************************************************
---------- Forwarded message ----------
Date: Thu, 16 Nov 2006 16:53:19 -0800 (PST)
From: Robert Peterson <peterson_at_mbi.ucla.edu>
To: ammrl_at_ammrl.org
Subject: AMMRL: Sumitomo helium compressors
Hi everybody,
We have three Bruker cryoprobes that range from two to four years old. The
two older helium compressors have each died after around three years of
operation. The first one needed its capsule replaced, and I suspect the
second one will also (it just died so I don't know yet). This repair is
quite expensive - in the ballpark of $10,000. Of course there are many
other things that can go wrong and most of them are not quite so
expensive.
In talking to several people I have gotten the idea that these compressors
usually run for around three years before breaking down. It would be very
useful to have a realistic estimate of their average annual maintenance
cost. The annual maintenance cost of cryoprobes is quite high because of
the mandatory annual service. I'm starting to wonder if the cost of
maintaining the compressors, after the first three years, is of the same
order of magnitude as the annual service.
I would like to tap into the collective experience of the group to get an
estimate of how often they break down, how much is the average repair
cost, and what is their average lifespan. Thanks in advance. I'll post a
summary of the responses.
-Robert
----------------------------------------
Robert Peterson, Ph.D.
Facility Manager
MBI-DOE Biomolecular NMR Facility
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax: (310)825-0982
peterson_at_mbi.ucla.edu
----------------------------------------
Received on Tue Dec 12 2006 - 13:24:15 MST