COMPRESSOR SUMMARY
1. We have used a Gast model 4HCJ-700P50Y-1 oil-less compressor set
(i.e. it includes a pressure vessel) since 1985. After 7 years the bearings
failed and we replaced it with a new, identical motor-compressor unit,
costing then about 300 pounds. The set drives two spectrometers, one with a
sample changer. It thrives on neglect, only requiring the water to be
drained out of the pressure tank every so often. You can, of course, buy a
gadget for doing that task as well. I'd recommend it to anyone.
2. We have been using a Powerex 3HP rotary scroll compressor along
with an Arrow refrigerant drier, 30 gallon steel tank, and Balston 75-20
drier for about 1-1/2 years and have had no problems with this whatsoever.
Our system provides insert/eject/spin air for high resolution experiments
as well as for CPMAS on a Bruker AMX 400. I wrote a letter to the NMR
Newsletter (formerly TAMU) describing our system in detail, and it came out
in the July 1995 issue.
3. I have a Jun-Air 4000 unit, 4 HP. We bought it directly from
Jun-Air, Buffalo Grove IL 708-215-9444.
>It is an oil-less, reciprocating piston design on a tank with sound enclosures.
>It was originally purchased with the molecular sieve regenerating air
>dryers, however the dryers could not handle the moisture at the maximum
>air capacity. We replaced them with a normal refrigerated air dryer.
>The compressor units (2 HP each) are moderately reliable, but far from
>satisfactory. Based on my experience, I do NOT recommend Jun-Air systems
>to our customers. The unit is 4 years old. Purchase price $5400 In four
>years I have replaced 3 compressor units at $850 ea. for a rebuilt unit
>with exchange.
>Additionally, under the original warranty, the entire unit (2 compressors
>and tank) was replaced once.
>My opinion is that the Jun-Air units are overrated in the deliverable air.
>This is a common game in the air compressor business. The replacement
>parts cost is quite high for the comsumables such as filters, etc. Service
>is responsive on the phone, but most problems are resolved by replacing
>compressor units.
4. Buy a Liquid Nitrogen transfill storage dewar and run off of that.
We got of tired of fulling around with dryers and its better low temp VT.
5. For most of my career I have used oil based Worthington compressors
with various traps, filters and vibration dampers. At Purdue I arrived to a
compressor which had a first rate oiless compressor with teflon lined
pistons, etc. Bob was very careful to buy a unit with extra capacity for
our needs, including a dehumidifier to preclude collection of water in the
lines. These units were popular with telephone company installations when
they would be required to operate unattended for long periods of time. I
do remember having problems with the dehumidifier and the pump itself. In
spite of careful planning the pump just didn't have the life expectancy
planned for--probably because the duty cycle was much higher than
anticipated.
At GE we used a Worthington with filters. In Applications we never had a
probe long enough to notice the ugly background. The pump caused a great
deal of floor vibration when it operated. Now I use nitrogen exclusively.
By the time you factor the cost of electricity for the pump and the capital
expense of the pump, the cost of nitrogen boil off is not prohibitive.
Nitrogen is also clean and dry and it arrives without pressure modulation
resulting from mechanical pumping. This permits continuous temperature
preregulation of vt carrier gas by FTS type coolers for good long term
performance.
6. More grist for your mill. We have Kaeser air compressors and they
seem to work fine. We maintain a service contract and the local distributor
services them on a schedule. We haven't had any problems. The only weird
thing is that one is oiless and one isn't and they are plumbed in parallel.
Go figure. Thus we do have oil in the lines and oil traps at each magnet.
We did have oil get into the flow gauge of the VT air which played havoc
with the VT. But the compressors work fine.
7. We are using GAST compressors. Three 7HDD generate enough air to
run our four NMR instruments. We do have two air tanks as buffers, run the
air at 80 - 100psi into an air cooler, where we get rid of most of the
moisture and afterwards dry it down in a cycling Balston air dryer. This
dryer requires about 20% of the incomming air in the reflux to dry out the
unused column.
I can not say that we have no problems with this system, but it provides us
with dry air and keeps us goiing.
The compressors wear out after about 2 to 3 years of usage and need to be
replaced by either a refurbished or new one 800 - 1000 $. We have been
continuosly growing in our department and the system will be to small for
any further additions.
Answering your questions:
1. GAST compressor 7HDD, 1.5HP
P.O. Box 97
Benton Harbor, MI, 49023-0097
616-926-6171
2. James Watson Company
29 Doran Ave
Marietta, GA, 30060
770-422-1154
3. The over all usage for the first unit is 11 years, the bigger unit was
added 5 years ago, including the Balston air dryer
8. We don't run,operate, maintain our own air supply (well, we do
"treat" the air and remove water, etc.). Our air is supplied by the campus
Facilities department. They have HUGE compressors just for this purpose (1
to 2,000 CFM at 100 psi if memory serves). I have no idea what they are
using but assume that it is quite a bit bigger than your needs.
9. I use oilless compressors for air supply to my NMR machines, both
for spin/lift and probe cooling.
10. I use HPC compressors. We have had some problems over the few years
since our unit was set up with compressed air. Reliability is one of the
main problems. We have got round this by using 2 x HPC KCT 401 compressors
with vertical air receivers and 2 x HPC 13 cfm dessicant dryers
The compressors are rated at 2.2kw and deliver 9.7 cfm at 8bar
They supply a common air line supplying 2 high field NMRs
Bruker AMX500
Varian UnityPlus 600
We use 2 compressors as a "fail-safe" (one compressor can cope with the load)
We have had this set up for 2 months now but over the last month we have
not had any problems. A cool, well sound-proofed plant room sited not too
far from the NMRs is ideal for the setup. The one major problem we have
experienced was due to the heat in our plant room.
I understand that HPC is a German company but have outlets world wide. You
would need to find your nearest reseller. If you can trace your nearest HPC
facility they will recommend a reseller/service/installer.
11. We use Ingersoll-Rand piston units. The performance is
satisfactory, and the design is mostly lubricated. The "oilless" part of
the piston assemblies is easily rebuilt at about 24 month intervals. The
units are water cooled. The model is one of their Series-30 units. There
are four cylinders on our units, in two banks. It is possible to run one
set and work on another without turning off the air.
Dr. Joseph Vaughn, Manager NMR Facility Chemistry Department
Florida State University
Tallahassee, FL 32306
Phone 904-644-3334
-9636
Fax 904-644-8281