Vacuum pumps

Claim 2

An oil-sealed mechanical vacuum pump having two or more stages comprising means for supplying oil to the pump including a duct, a fluid flow control valve in the duct, a pressureresponsive movable member in the control valve which presents an impedance to the flow of oil that is a function of the mean inlet pressure of the pumped gas to any one of the stages except the first, the impedance being variable by the action oF this pressure on the movable member of the fluid control valve.

Claim 3

An oil-sealed mechanical vacuum pump having two or more stages as claimed in claim 1, the last stage including an inlet and a final outlet, in which the impedance of the said duct to the flow of oil is a function of the mean pumped gas pressure in the inlet of said last stage of the pump.

Claim 4

A pump as claimed in claim 1, one stage being a control stage for the oil supply means, the inlet of the oil supply controlling stage being isolated from the outlet of the immediately-preceding stage by means of a non-return valve.

Claim 5

In a pump as claimed in claim 3, an oil reservoir, said fluid flow control valve including a seat for its pressure-responsive movable member, spring means biasing the movable member away from its seat, a conduit through which oil is supplied through the space between the valve seat and the movable member continuously while the pump is working, a conduit establishing communication between the outlet side of the seat and the reservoir, and said pressure-responsive movable member being biased towards valve closing position on the seat by a control pressure of the pumped gas which is variable as a function of the pressure in the inlet to the oil supply control stage.

Claim 6

A pump as claimed in claim 3 in which the displacement of the oil supply controlling stage is appreciably smaller than that of the immediately preceding stage.

Claim 7

A pump as claimed in claim 2, in which the displacement of the last stage is of the order of one-twentieth of that of the immediately-preceding stage.

Claim 8

A pump as claimed in claim 6, in which the valve member is movable with a flexible diaphragm of which one side is exposed to a reference pressure and of which the other side is exposed to the control pressure of the pumped gas.

Claim 9

A pump as claimed in claim 6, in which the valve member is movable with a plunger defining a movable wall of a chamber having its interior in communication with the inlet to the outlet stage, the plunger being sealed to the chamber in a fluid-tight manner and having its outer surface exposed to a reference pressure.

Claim 10

A pump as claimed in claim 6, in which the valve member is movable with a flexible diaphragm of which one side is exposed to the oil inlet pressure, and in which the other side is exposed to the control pressure.

Claim 11

A pump as claimed in claim 6, in which the valve member is biassed into contact with an aneroid capsule having its external surfaces exposed to the control pressure.