The present invention relates to pumps in general, and more particularly to plunger-type pumps.
There are already known and in widespread use various constructions of pumps which, depending on the requirements of such pumps, such as the pressure conditions, types of media to be pumped, volume to be pumped, and whether the operation is to be intermittent or continuous, have different shapes and operating parameters. Among such pumps, there has been already proposed a plunger-type pump in which a plunger is mounted in a pump housing and extends into a pumping chamber defined by the latter for reciprocation therein. In a pump of this type, one-way valves are to be provided both at the inlet side and on the outlet side of the pump and, in this connection, it has already been proposed to construct the inlet valve as a valve sleeve which is mounted on the plunger for movement longitudinally thereof and for limited reciprocation therewith. Then, the sleeve valve subdivides the pumping chamber into a suction space and a pumping space, the former surrounding, and the latter being located within the sleeve valve.
Pumps of the latter type achieve excellent results while being simple. However, experience with this type of pumps has shown that the seaing of the interface between the sleeve valve and the plunger leaves much to be desired. Usually, such a seal is constructed as an interface seal and is achieved by selecting the proper tolerance between the inner surface of the valve sleeve and the outer surface of the plunger, and by properly selecting the materials of the two components which bound the interface. While, under many circumstances, this type of seal may work to satisfaction, it has been established that this type of seal cannot be used with certain media to be pumped, particularly with aggressive media. A further limitation to the use of this type of seal resides in the fact that this type of seal can only be used up to a certain pressure existing in the pumping chamber. While it is not absolutely impossible to properly select the tolerances between the abovementioned surfaces for any pressure region or pressure differential existing across the sleeve valve, it has been found that the high precision which is required for high pressure involves costs which are prohibitive.