Содержание

Priming Centrifugal Pumps

Терпигорева В.Д., Матвеев С.Д.

      There are 3 methods: (a) installing [§ 5, 3] a foot valve and filling the suction pipe and pump casing with water from the discharge column; (b) using [§ 5, 3] a vacuum pump, or other means of exhausting air from the suction line and pump casing, and filling them with water from the sump; (c) providing a head on the suction, when a pump takes water from a dam. Foot valves are widely used for small pumps, but are not reliable, as they are apt to leak and wear out rapidly in acid water. A pump with a foot valve will operate automatically with safety, but often fails to start when the valve becomes leaky. Hence, foot valves are not recommended for mine service.
      A priming pump is used for most centrifugals. It is started by a switch operated by a float in the sump, and exhausts the air from the centrifugal, thus drawing water from the sump through the suction pipe and pump casing, and thence through a valve into a priming chamber, which contains a float. When water enters the chamber, the float rises and closes the priming switch, which starts the centrifugal pump motor. The motor having been accelerated [§ 5, 2, в)] a contact is automatically opened, stopping the priming pump. When the centrifugal begins to run, the priming valve is closed by the pressure from the pump, the water from the priming chamber drains out, and the priming switch opens them when the switch is open. These devices consist of a vacuum regulator, which opens the circuit if the vacuum exceeds a predetermined value, and a pressure regulator, opening the circuit when the pressure in the discharge line falls below a predetermined pressure.
      Priming pumps may be either wet or [§ 4] dry. Wet priming pumps are in common use, but the water must be clean and free of acid [§ 6, 2]. Dry priming pumps require less power. A trap must be interposed, to prevent the water from entering the cylinder; a barometric loop serves the same purpose. The most efficient trap, widely used [§ 5, 2] with pumps handling acid water, is a chamber in which a float operates an air valve. This valve opens when the water enters the chamber, causing the vacuum to break, thus preventing water from entering the pump [§ 5, 2]. The chamber is placed above the pump and connected to top of the casing of a single-stage pump, or to top of the first stage of a multi-stage pump.
      The remaining stages need not be primed.
      An up to date pump room usually contains several multistage centrifugal pumps. For such a pump room it must be provided with an 8-ton travelling crane, to facilitate repairs. The suction pipes drop directly into the sump, and can be lifted out by the crane. For station pumps, solid concrete foundations are well worth while. They should be true, of good materials, and only one end of pump bed-frame should be bolted down, the other being left free [§ 5, 2, в)], to allow for expansion.
      Gathering pumps, designed to be moved frequently from place to place, are preferably of the self-priming centrifugal type. Generally, the types capable of pumping continuously a mixture of air and water are less efficient and more subject to wear than those pumping water only.

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