CYLINDER AND HEAD ASSEMBLY

for transfer are designed to pump 200 gpm at 50 psi. The typical rotary vane pump consists of a cylinder and head assembly, rotor and shaft assembly, and a pressure control valve. CYLINDER AND HEAD ASSEMBLY. —The cylinder (pump casing) houses and provides a working area for the rotor and shaft assembly. The cylinder is machined to form an egg-shaped cylinder bore. The inlet and discharge ports are cast integrally with this section of the pump. The pressure control valve, located on the top of the pump, is cast integrally with the upper portion of the cylinder bore. Each side of the cylinder has machined recesses to ensure perfect fit of the cylinder heads. The cylinder heads (fig. 4-1 1), one for each side of the pump, house the ball bearings and mechanical seals. An O-ring is installed between the cylinder heads and the cylinder to prevent leakage. The ball bearings, located in the bearing housing within each cylinder head, support and ensure free rotation of the rotor and shaft assembly, and maintain the proper clearance between the rotor and upper position of the cylinder bore. A bearing cover, with a grease fitting at the top and a grease relief fitting at the bottom, is bolted to the end of each cylinder head. The mechanical seal installed in each head pre- vents leakage of fluid along the shaft into the bearing housing. A telltale drain hole, located directly under the bearing housing, is provided on the underside of each head. These holes are intended to serve as an indication of leakage by the mechanical seal. Figure 4-11.—Rotary vane pump cylinder head. ROTOR AND SHAFT ASSEMBLY. —The rotor and shaft is a pressed fit assembly held in place by tapered pins. The rotor is centered in the upper portion of the oval shaped cylinder bore. The rotor has an even number of equally spaced slots that provide the working area for the sliding vanes. Holes are drilled through the rotor and shaft, one between each set of opposing slots, for the installation and working area of the push rods. The sliding vanes are made of palamite. Relief grooves are provided on the forward face of the vanes to allow the escape of liquid trapped between the vanes and the slots in the rotor. NOTE The vanes must face the direction of rotation to allow the escape of fluids into the discharge port. The pump shaft connects to a gear reducer shaft by a flexible coupling. The opposite shaft of the gear reducer is connected to the shaft of the drive motor, also by a flexible coupling. The purpose of the gear reducer is to mechanically reduce the motor rpm to match the rated rpm of the pump. PRESSURE CONTROL VALVE. —The pres- sure control valve is provided to prevent buildup of excessive pressure that might damage the pump or associated equipment. When over-pressurization occurs, the valve directs fluid from the discharge side to the suction side of the pump. It is spring-loaded closed. An adjustment screw adjusts spring tension on the valve disc. Relief pressure is determined based on pump application and piping design. The adjustment screw has a locknut to lock it at the set pressure. The pressure control cap is screwed on the cover to protect the adjustment screw threads. THEORY OF OPERATION. —The rapid rotation of the shaft and rotor forces the vanes in sliding contact with the cylinder bore by centrifugal force and by push rods. The passage of the vanes through the lower portion of the cylinder bore draws fluid into the pump, and at the same time, forces it out the discharge port. Rotary vane pumps are positive displacement pumps. This means they will pump air, which creates a vacuum, causing liquid to be pulled into the suction side of the pump. MAINTENANCE. —Maintenance on the rotary vane pump is done in accordance with PMS and the 4-15