6
2.6
Electrical Power
2.6a 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. Consult your local electrical
codes if you have doubts.
2.6b Overload Protection.
Motor thermal overload protection is made available by the motor manufacturer as an aid to minimizing 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 rest 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.
2.7
Vacuum Connections
The 2090/2085 vacuum pumps come with NW25 ISO vacuum flange with a 3/8"-18 NPT threaded I.D. Hinge
clamps and centering assemblies should be implemented if using the flange connections. If using the 3/8”-18 NPT
threaded connection, a suitable quality liquid/paste thread sealant should be used. Since both 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 process be kept as short as possible. The
exhaust plumbing will act to muffle pump noise. The exhaust vent line will allow gases and vapors pumped
through the pump to be piped from the work area into a hood. Be sure to safely exhaust the process vapors with
consideration to worker health and fire safety.
2.8
Traps
2.8a The need for a Trap
The use of Teflon coated aluminum heads, Teflon liner over diaphragms and stainless valves allows the pumps to
handle mildly corrosive solvents, acids and bases. 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.
When a heavy load of vapor is evolved from the vacuum process, a cold trap is recommended to help prevent
damage to the pump mechanism.
The symptom of a high vapor load is if you have droplets of liquid coming out of the exhaust port. If you see
droplets of water, Welch recommends you use a cold trap to capture the water before entering the pump or dilute
the water vapor stream by adding dry nitrogen to the gas flow. Please call our customer service department for
additional information at (847) 676-8800.
