Abstract: A screw vacuum pump which allows reduced power, lower inside gas temperature, and reduced discharging time. The pump has a pair of screw rotors rotatively engaged with each other in a pump casing to discharge a gas along a longitudinal direction of the pump. Each rotor has three types of helical teeth serially located in a longitudinal direction of the rotor and different from each other in theoretical displacement volume. A bypass conduit communicating with a delivery side of the pump is connected via a first check valve to a first intermediate space defined between the first helical teeth and the second helical teeth and via a second check valve to a second intermediate space defined between the second helical teeth and the third helical teeth. The gas is compressed at the third stage to half the first stage volume before a discharge port opens.

Abstract: An object of this invention is to prevent drop of life of a bearing by an axial force when using a pump as a compressor. In a vacuum pump 1 compressing and discharging gas in a direction of a rotor axis by rotation of screw rotors 3, 4 engaged together which are supported rotatably in a casing 2, balance pistons 13, 14 are disposed on shafts 6, 7 of said screw rotors at inlet side of said casing. The balance pistons separate a receiving section 17 at area of the screw rotor and a pressurizing section 16 at area of the balance piston, and a thrust force of the screw rotors at a pressurizing condition is canceled by acting the discharge pressure in the pressurizing section. The pump is used as a compressor when the discharge pressure is acted on the balance pistons 13, 14. When the pump is used as a vacuum pump, air at discharge side is sucked as cool air through a cooler toward a place near to the discharge side of the receiving section 17 at area of the screw rotor.

Abstract: A dry vacuum pump assembly that includes a casting having an inner chamber, an inlet and an outlet communicating with the inner chamber, a pair of right and left handed screw rotors positioned in the casing, each screw rotor having a cross section formed by a Quimby curve, a circular arc, and a quasi-Archimedean spiral curve, the pair of screw rotors intermeshing with each other to pump a process gas pumped from the inlet to the outlet. The pump assembly further includes a nitrogen-supplying tube that communicates with the inner chamber at a position near the outlet in the casing, and an external pipe that connects the outlet to a scrubber or a trap which external pipe is straight and does not include a silencer.

Abstract: A feed pipe 26 for a sealing water is connected to a housing of the pump to communicate with an enclosed chamber which is defined between a position in which a helical seal line of screw rotors 17 isolates the enclosed chamber from a suction port 15 of the pump and another position in which the enclosed chamber begins to open to a discharge port 24. Alternatively, a feed pipe for the sealing water is connected to the suction port 15 of the vacuum pump, and the feed pipe 26 is provided with a valve V which opens when the suction pressure of the sealing water becomes lower than −380 mmHg.

Abstract: A dry vacuum pump that includes a casting having an inner cylinder communicating with an inlet and an outlet of the pump, shafts supported by the casting, spiral toothed parts formed on the shaft a plurality of screw rotors each of which includes the shaft and the spiral toothed parts received in the inner cylinder intermeshing with each other. Timing gears each of which are attached to the respective shafts of the screw rotors that intermesh with each other. Locking mechanisms for fixing the timing gears to the shaft. Both of the shaft and the toothed part are made of spheroidal graphite cast iron containing 20 to 30 wt % of nickel are cast integrally.

Abstract: The moment Mo of unbalanced forces Fr of a screw rotor A1 is reduced by adjusting the number of thread leads of a threaded portion 2 of the screw rotor A1 to (an integer +0.5). The amount of unbalance for keeping a state of dynamic balance thereby decreases, and the drilling of a thread e for keeping the state of the dynamic balance is made easier.

Abstract: A discharge side housing 3 has a third cooling water chamber 19 communicating with a first cooling water chamber 7 of a main housing 1 through a cooling water passage 26. The third cooling water chamber 19 is connected to a cooling water outlet pipe 27 which is connected to an inlet port 28a of a three-way valve 28. The three-way valve 28 has a switching port 28b which can communicate with a pipe line 29 connected to the first cooling water chamber 7. The three-way valve 28 has an outlet 28c connected to a pipe line 30 which communicates with a second cooling water chamber 22 of a suction side housing 2. The second cooling water chamber 22 is connected to a cooling water discharge line 31 provided with a flow control valve 32 allowing a back pressure for a cooling water flowing thereinto.

Abstract: A pressure-resistant explosion-proof electric motor (44) is surrounded by a double casing comprised of inner and outer cases with a motor-cooling oil passage (54) formed therebetween. A flange (26) is detachably fitted to the top surface of a tank to hold the electric motor (44) in the tank. A downwardly-extending pipe (28) is at an upper end fixed to the flange and at a lower end connected through a terminal box (30) to the electric motor (44). A centrifugal pump (67) is fixed to the underside of the electric motor (44) to have its rotary shaft connected to the output shaft (60) of the electric motor (44). A motor cover accommodates therein the electric motor and the terminal box (30) in a watertight manner. A protective pipe (71) extends from the flange (26) to the motor cover (69) and accommodates therein the downwardly-extending pipe (28) in a watertight manner. A cooling oil is circulated through the motor-cooling oil passage (54) to cool the electric motor.