The pressure regulator and pressure dial gauges are attached to the
discharge port. The pressure regulator allows discharge pressure to
be set between atmospheric and the maximum possible for the pump
model. Discharge air is filtered and noise is muffled with a filter.
Note: Adjusting either the pressure or vacuum regulators will
affect the performance of the pump.
PROPERLY IDENTIFY THE INTAKE AND
DISCHARGE OF THE PUMP
WARNING!: Never Block The Discharge Port.
If the exhaust is blocked, pressure will build- up
in the pump above its rated operating pressure.
Be sure to call Welch technical service prior to start-up at (847)
676-8800 if you have any questions.
II-6. ELECTRICAL POWER
lI-6a. Power Source Review
Review the power source and the motor rating to be sure they agree
in voltage, phase, and frequency. Serious damage may occur to the
motor if it is connected to an improper voltage. All Welch pumps
must be grounded. Grounding reduces the risk of electric shock in
the event of an electrical short circuit. The plug must be plugged
into a properly grounded outlet. Consult your local electrical codes
if you have doubts.
ll-6b. Overload Protection.
Motor thermal overload protection is made available by the motor
manufacturer as an aid to minimize motor failure.
Overload protection is a standard feature on both 50 and 60 Hz
single-phase-motors. The motors have automatic overload
protection. Automatic reset protection is designed to reset itself
after a predetermined cooling period. If the fault to the drive remains
unaltered, the motor will cycle on and off until the fault is corrected.
II-7. VACUUM CONNECTIONS
All pressure/vacuum pumps come with intake and discharge hose
barbs which accept 1/4" ID rubber pressure/vacuum hose. Hose
clamps should be used to hold the hose in place. Since all three
models operate in the viscous flow regime, the small diameter of
the hose will generate minimal conductance loss. For best results,
Welch recommends the length of the tubing between the pump and
the chamber be kept as small as possible.
II-8. VACUUM AND PRESSURE GAUGES
All models of pressure/vacuum pumps come with dial gauges
mounted on the regulator assemblies. The vacuum gauge gives
negative pressure - that is pressure below atmospheric. The reference
point for the vacuum gauge is atmospheric pressure.
The pressure gauge gives pressure above atmospheric. The
reference point for the pressure gauge is atmospheric pressure.
Please keep in mind that atmospheric pressure tends to vary from
day to day. As a result of this variability, the dial vacuum gauge
will indicate slightly different maximum vacuum readings from
day to day.
II-9. TRAPS
II-9a. The need for a Trap
The pumps will handle humid air. All wetted aluminum parts are
treated for corrosion protection from moisture. All other wetted
parts are stainless steel. A plastic trap with a ball check valve is
attached to the regulator assembly to prevent water condensate from
accidentally being ingested into the pump. If there is a chance liquid
may be drawn from the process under evacuation, Welch
recommends a liquid trap be placed between the process and the
pump. A simple liquid trap is a filtering flask. See figure below.
When a heavy load of water vapor is evolved from the vacuum
process, a cold trap is recommended to help prevent damage to the
pump mechanism. The cold trap, immersed in a suitable Dewar
flask, is installed so that the water vapors may come in contact
with the surfaces of the trap and condense. Commonly used
refrigerants are liquid nitrogen or dry ice and acetone or alcohol.
Dry ice provides sufficient cooling to freeze out most heavy water
vapor loads. A variety of cold traps are available from Welch. Please
call our customer service department for additional information at
(847) 676-8800.
WARNING!: The pump is not recommended for
pumping acid, base or organic vapors or gases.
Serious damage to the pump will shorten the
pump’s service life. In addition, pumping
flammable vapors or gases can lead to serious
safety hazard leading to fire or explosion.
lI-9b. The Care of a Trap
When using a cold trap the refrigerant should be maintained at a
high level in the flask to keep the trap at a uniformly low
temperature. If the trap is rewarmed it may allow re-evaporation of
the condensate. The refrigerant add tube on the liquid nitrogen trap
should not be obstructed as the refrigerant boil-off can pro- duce
dangerously high pressures. If the trap becomes saturated it should
be disconnected from the system, drained, and cleaned. An increase
in pressure in the vacuum system will normally indicate that the
trap has become saturated. To clean the trap, remove the trap from
the system and allow the trap to warm up and rinse off the
condensate with a suitable solvent in a fume hood. Thoroughly
clean and dry the trap before reinstalling into the system.
Ill. OPERATION
Ill-1. STARTING PROCEDURES
Pressure/Vacuum Pump
Intake Discharge
Discharge
Suction
Filtration Manifold Liquid Trap
