Rebuilding
the
Welch 1402
Vacuum Pump

Supplement 1

Tolerance

Setting the space between the Intake Ring and the Intake Rotor on a Welch 1405 Vacuum Pump.

(The Welch 1402 Vacuum Pump has similar parts and the procedure is the same.)

S1

To accurately set the space between the Intake Ring and the Intake Rotor you will need a tool called a feeler gauge.

An auto parts store might be a good place to find one.

A feeler gauge is a series of metal strips that are different thicknesses.

S2

You will need something to set the pump body on so that you can move the Intake Ring and the Intake Rotor and still tighten the screws that hold the Large End Plate to the Intake Ring.

A short length of PVC pipe will allow the pump body to lie flat even with the shaft.

Loosen the screws holding the Intake Ring to the Large End Plate. There is a screw underneath the Large End Plate Cover that is easy to miss.
Adjust the space between the Intake Ring and the Intake Rotor by gently tapping the Intake Ring with a softer material like a rubber mallet or a piece of wood.
Insert the proper thickness feeler gauge in the space between the Intake Ring and the Intake (contd.)

(contd.) Rotor.
Adjust the space.
Tighten the screws holding the Intake Ring to the Large End Plate.
If the screws at the bottom of the pump are tightened first they will hold the Intake Ring in place while the other screws are tightened.

When the space was set to 0.0015 inches the shaft would not turn. When the space was set to 0.002 to 0.003 inches the shaft turned fine and the pump showed steadily decreasing vacuum when it was tested with a vacuum gauge.

Warning: If there is too much space between the Intake Ring and the Intake Rotor you may feel suction on the intake of the pump but the vacuum gauge may show no vacuum.

S3

Use an allen wrench or thin metal rod to be sure the shaft turns freely before reassembling the pump.

Reassemble the vacuum pump and test it with a vacuum gauge.

See the Supplement on Vacuum Gauge.