Rebuilding
the
Welch 1402
Vacuum Pump

Supplement 3

Vacuum Gauge

(Revised 10/29/15)

M1

To test the rebuilt pump you need a vacuum gauge. They can be expensive.

You can buy an inexpensive vacuum gauge (about $25.00) at your local NAPA Auto Parts store. The part number is 700-1068

This vacuum gauge will tell you whether or not the vacuum pump is pulling a vacuum but the gauge will not tell you whether or not the vacuum pump reaches the manufacturer specified ultimate vacuum of 0.0001 torr (models 1402 and 1400) because the gauge does not go that low.

If you have a vacuum gauge that measures below 1 torr, you can measure the vacuum on your pump.

M2

If you have a vacuum gauge that measures below 1 torr, you can measure the vacuum on your pump.

You will need vacuum tubing and hose clamps.

Vacuum tubing is tubing with a thicker wall so the vacuum cannot pull together the sides of the tubing.

M3 & M4 & M5

Attach one end of the tubing to the inlet on the vacuum pump, use a hose clamp to tighten it.

Attach the other end of the tubing to the probe from the vacuum gauge, also use a hose clamp to tighten it.

M6
Turn on the vacuum pump and turn on the vacuum gauge and wait for the vacuum to go down. Compare the vacuum reading you get to the manufacturer specification for the pump.

For this vacuum pump if the specification is 1 x 10 ^ -4 torr or 0.0001 torr this vacuum pump has some more work to do before it reaches the specification.

Even a tiny vacuum leak will cause problems so use a short length of tubing and tighten the hose clamps.

If the tubing is larger than the vacuum inlet or the vacuum gauge probe the hose clamps may not be able to tighten it enough to close a leak. You want the hose diameter to be slightly smaller than the vacuum inlet and the vacuum gauge probe.