Dear AMMRL:
I have been asked to design a new compressed air system for five spectrometers
(two 400 MHz and one 800 MHz liquid state, one 400 MHz and one 600 MHz both
liquid-state and solid-state, all Bruker except one of the 400 MHz liquid-state
spectrometers) to replace parts of our obsolete reciprocating system. We have
only used oil-less compressors for many years and are continuing with that.
Scroll compressors seem to be the best choice in terms of price, complexity,
and availability, so we have decided upon using them.
The problem is that while 116 PSI scrolls are less expensive up front because
lower pressure provides greater flow allowing for usage of fewer scrolls and
will cost less for maintenance compared to 140-145 PSI scrolls, making them
very attractive, I don’t think they can provide the pressure that we need.
Our original oil-less facility-wide (reciprocating) system used a pressure
range of about 135-115 PSI, which I think is still viable now. (On the current
system we use the lowest possible range, which is 155-135 PSI, but regulate
at 110 PSI at the compressor room outlet. We have an extensive piping system
to reach the spectrometers housed in two adjacent buildings.)
The reasoning behind the choice of maximum pressure is: pressure loss due to
the differential (20 PSI standard, which I understand is required to keep the
compressors from burning out by turning on and off too often), across the
compressor system dryer (~5 PSI), requirement for a slightly higher pressure
at the system regulator inlet than outlet (although it may be possible to
cheat on this due to the differential and set the regulator to the lowest
pressure that goes into it since this only occurs for a small fraction of
the time?), along the piping (not known, budgeting ~ 5PSI), across additional
dryers at the spectrometers (~5 PSI). With range 135 – 115 PSI, this gives
110 PSI minimum into the regulator and regulator setting of 110 PSI, at least
105 into the spectrometer room where a regulator there is set to 100 PSI if
a dryer exists, and at least 95 PSI are available to set the final regulator
into the spectrometer to between 80 and 90 PSI. We have one of the (solid-state)
spectrometers set at 90 PSI and an upstairs liquid-state spectrometer with
no ballast tank set at 82-83 PSI.
For 116 PSI compressors the range would be 116-96, 91 PSI minimum into the
system regulator and regulator setting of 91 PSI, at least 86 into the
spectrometer room, where there is not extra for regulation or dryers, and it
seems that even 80 PSI could not be set reliably at the spectrometers.
For anyone willing to help who has been through this type of planning recently:
do my calculations seem reasonable or wrong? Has anyone made a single central
facility-wide system for several spectrometers successfully with 116 PSI scrolls?
Margaret
Dr. Margaret A Eastman
NMR Facility Manager
Department of Chemistry
Oklahoma State University
Stillwater, OK 74078
margaret.eastman_at_okstate.edu
(405)-744-7544
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Received on Tue Jun 09 2026 - 13:25:34 MST