DAU-20 Instruction Manual
8
5 Pump Performance
5-1 Ultimate pressure
"Ultimate Pressure" mentioned in Catalog and this Instruction Manual means "the lowest pressure
obtained by a pump in the status that no gas is filled from the pump inlet port (idling operation status)
”.
Ulvac is measuring the pressure by connecting a film-type (diaphragm type) vacuum gauge to inlet
port of the pump.
Please note that the indicated value of the pressure may be different depend on the type of the
vacuum gauge.
Ultimate pressure of the actual vacuum devises usually higher pressure than the catalog value.
Reason of this phenomena is as follows.
(1) The mounting location of the vacuum gauge is far from the pump and steam and various kinds of
gases generated from drops of water or rust that attached to the inner wall of the equipment and
piping make the ultimate pressure higher.
(2) Ultimate pressure becomes higher in case there is resource of gas such as vacuum leakage in
the vacuum route.
5-2 Exhaust velocity
Flow rate of the diaphragm type dry vacuum pump varies according to the type and pressure of gas to
intake. Generally, it shows the maximum exhaust velocity in atmosphere introduction that becomes
lower little by little as the pressure becomes low.
In addition, the thinner diameter of piping and longer piping would make piping resistance large
resulting the slower discharge velocity.
Nominal discharge velocity of this pump shows the maximum when breathe dry air.
5-3 Power Required
Power to drive a pump is the sum of the work for rotating friction of the machine element (machine
work) and the work to compress air (work of compression). It becomes the largest in the vicinity of 3 x
10
4
to 10 x 10
4
Pa inlet pressure. When this becomes lower, work of compression is small and power
is consumed by machine work.