Welch has developed two pumps for high vacuum, mass spectrometry and
similar scientific instrument applications, providing effective backing
for hybrid turbomolecular and molecular drag pumps and gas analysers. The
Model 8111 (oil-free, two-stage diaphragm pump) and Model 2581
(dry-running Wob-L piston pump) provide high pumping speeds below 20mbar,
the former achieving a flow rate of 32 litre/min and 1mbar ultimate
pressure, the latter 100 litre/min and 5mbar.
The 8111 features a tangentially fixed diaphragm and highly efficient
forced valve operation, with the suction valve located at the very edge
of the pump chamber, resulting in a very compact two-stage unit. The
aluminium bodied 2581 is similarly compact, with a footprint of just 19
by 32cm.