Special Applications

Systems for Sewage Pumps A pump handling sewage or similar liquids containing stringy material can be equipped with automatic priming, but special precautions must be used to prevent carry-over of the liquid into the vacuum-producing device.

One approach is to use a tee on the suction line immediately adjacent to the pump suction nozzle, with a vertical riser mounted on the top outlet of the tee. This riser is blanked at the top, thus forming a small tank. The top of the tank is vented to a vacuum system through a solenoid valve. The solenoid valve in turn is controlled electrically through electrodes located at different levels in the tank. The solenoid valve closes if the liquid reaches the top electrode and opens if the liquid level falls below the level of the lower electrode.

Another solution permits the use of an automatic priming system with a separate motor-driven vacuum pump controlled by a discharge-pressure-actuated pressure switch. An inverted vertical loop is incorporated in the vacuum pump suction line to the pump

being primed. This prevents the sewage from being carried over into the vacuum pump because this pump shuts down before the liquid reaches the top of the loop.

Systems for Air-Charged Liquids Some types of liquid have considerable dissolved gas that is liberated when the pump handles a suction lift. In such installations, an airseparating tank (also called a priming tank or an air eliminator) should be used in the suction line. One type (Figure 12) uses a float-operated vent valve to permit the withdrawal of air or other gas. Another common arrangement uses a float valve mounted on the side of the tank to directly control the starting and stopping of the vacuum pump. Unless the air-separating tank is relatively large and the vacuum pump is not oversized, there is danger of frequent starting and stopping of the vacuum pump in such a system. When sand is present as an impurity in the liquid, the air-separating tank can be made to also function as a sand trap.

Systems for Units Driven by Gasoline or Diesel Engines An automatic priming system using motor-driven vacuum pumps can be used for centrifugal pumps driven by diesel engines if a reliable source of electric power is available in the station. An auxiliary vacuum pump driven by a gasoline engine might be desirable for emergency use in case of electric power failure. Alternatively, a direct-connected wet vacuum pump with controls similar to those used in motor-driven automatically primed units is very satisfactory.

The choice of the priming device for a gasoline-engine centrifugal pump depends on the size of the pump, the required frequency of priming, and the portability of the unit. Most portable units are used for relatively low heads and small capacities, for use in pumping out excavations and ditches, for example. Self-priming pumps of various types are most satisfactory for this service and are preferable to regular centrifugal pumps.

It is possible to utilize the vacuum in the intake manifold of a gasoline engine as a means of priming or keeping the pump primed. The rate at which the air can be drawn from the pump in this manner is relatively low, so many of these units use foot valves. They are initially primed by filling the pump manually. Provision must be made to prevent liquid from being drawn over into the manifold.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

Get My Free Ebook


Post a comment