Combined water meters

An automatically acting switch valve for a combined water meters which has a main meter for measuring larger flows and a secondary meter for measuring smaller flows. The switch valve has a switch insert including a carrier with a central slide bolt fastened to it, a shut-off member displaceably guided on the bolt and urged into closed position by a spring, a sealing seat of greatly narrowed cross section provided with an elastic seal between the carrier and the shut-off member. An annular chamber receives the shut-off member and opens downstream. It has a cylindrical zone and an adjoining same a conically narrowing annular zone which terminates in a narrowed shut-off member retention step. The shut-off member has a disk-shaped rim the front part of which is contained, in the closed position of the valve, within the cylindrical zone of the annular chamber. The dimensions are so adapted to each other that the seal only frees the main-stream passage when the disk rim of the shut-off member moves up into the conically narrowed annular zone under the pressure of the water. Due to the construction of the invention, a weak, short restoring spring is required so that the switch valve can be made small and compact.

Combined water meters and automatically acting switch valves which serve for switching between a main meter and a secondary meter were used in the nineteenth century. They include a valve disk including a surface which is larger than the surface of the sealing seat of the main water stream. As a result, the differential water pressure acts on a smaller surface in a blocked passage and on a larger surface in an open passage in order to abruptly open the valve disk. In order to counterbalance for the differential water pressure when the valve disk is closed, suitable means are employed, for instance, gravity, spring force, etc. It is desired that the valve disk open and close in each case as suddenly as possible so that no errors in measurement will occur.

All switch valves having a closure spring have one problem in common. The restoring force of the spring increases linearly with an increasing path of opening of the valve disk. The ideal, however, would be a constant or even a decreasing restoring force, as is present in the above mentioned weight loaded flap valves. Spring loaded switch valves must therefore be provided with a spring which is as long as possible in order to keep the increase in force slight. This, however, runs counter to the so-called short construction length which is preferred today.