Screw pumps are extensively used in different branches of industry and agriculture for transportkng petroleum products, water, various types of emulsions, gas-liquid mixtures, bitumens, pastes, syrups, molasses, alkalis, suIfides, etc. They are competitive with centrifugal, piston, gear, and other types of pumps in many cases and are practically the only choice in the petroleum, chemical, and food industries. Screw pumps are used in shipboard fuel and oil pumping systems, loading and ballast systems, drying and fire protection systems, sanitary systems, etc. They can also be used as hydraulic system power pumps.A twin-screw sealed pump (Fig. 1) is described in a British patent [1]. Each screw consists of two pumping elements with right-and left-hand threads. The screws are located in a figure-eight-shaped barrel which is mounted in the cylindrical pump casing. Liquid is supplied to the screws through a suction nozz[e in the casing. The liquid flows into the barrel from both sides to the screw pumping surfaces. It is then discharged into the outlet header. The inner barrel with the screw pumping compartment also acts as the sealhag element between the suction and discharge sections.A twin-screw sealed pump developed in the Polish Peoples Republic (PNR) [2] is shown ha Fig. 2. It consists of casing 9, and right 12 and left 7 covers which are attached tothe casing by hoops 11 and 8. The hoops are tightened by screws 13. Shafts, passing through the left cover, are connected to pumping screws 10 by slotted couplings 1. Screws 10 rotate in bearings mounted in the right cover. Shaft 6 is connected to the drive train by coupIing 5. Glands, consisting of packing followers 3 and packing 2, are provided on shafts 4 and 6. The hoops and right cover with the pumping screws must be removed for pump inspection and repair. Dismantling, cleaning, and assembly of the pump takes only a short time.
