Welch 8890, Руководство пользователя

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6
WARNING
Never block or impede air flow from the exhaust port. High pressure
can build up within the oil reservoir if the exhaust flow is blocked.
Check frequently, especially if exhaust is piped out of the building.
1.6 Electric Power
Compare the pump motor rating, printed on a label on the side of the motor, to the power source, to be sure they
agree in voltage, phase, and frequency. Pump installation must comply with local electrical codes which dictate
appropriate protection devices such as fuses or circuit breakers. We strongly suggest that you learn the location
and operation of the circuit breaker or fuse protecting the electrical outlet for the pump so that you can react
quickly in the event of an emergency.
The vacuum pump motor is factory wired to for 115 V for models which operate from 60 Hz, and
220 V for models which operate from 50 Hz. The motor wiring can easily be changed for operation at a voltage
different than that set at the factory. Follow the motor wiring schematic diagrams in Section 3-2 – Motor Power
Specifications and Special Features.
Identification Symbols:
CAUTION
Only a qualified technician should attempt motor rewiring. Motor lead wires can
be accessed by removing the four screws on the top lid of the motor junction box.
1.7 Vacuum Connections
The pump inlet is equipped with a hose barb nipple for connection of 3/8 in. ID hose. It is located next to the
pump handle.
The choice of connections and fittings can have a very marked effect on the pumping speed at the vacuum
chamber. Any connection placed between the pump and the chamber creates an impedance to the flow of gas.
This is particularly true at low pressures in the millitorr range where the gas flow is substantially molecular in
character. The gas flow is then dependent upon the kinetic activity of the molecules to bring it to the pump
intake.
The conductance of a tube is proportional to the cube of its diameter and inversely proportional to its length.
Therefore, connecting lines should be as large in diameter and as short in length as practical. For best results the
connection tube should be at least as large as the diameter of the pump intake. To avoid a large reduction in
pumping speed at the vacuum chamber, the conductance of the line must be considerably greater than the speed of
the pump.
1.8 Vacuum Gauges
The type of vacuum gauge to be used in a system is determined largely by the pressure range to be measured. A
thermocouple gauge or a dial-type gauge, is recommended for measuring pressures in the range produced by this
pump. See Section 9 – Accessories.