Accumulator-reservoir device diaphragm control

In a substantially closed fluid circulating system, a pump which when in operation circulates fluid under pressure, said pump having inlet and outlet sides having regard to the direction of flow of fluid therethrough, said inlet and outlet sides representing respectively suction and pressure sides of the pump, an accumulator-reservoir device of the bootstrap type, a connection from said device to apply a fluid pressure to the suction side of said pump, a connection to said device from the pressure side of said pump to generate in said device during operation of said pump the fluid pressure applied to the suction side of said pump and to maintain fluid pressure in the system during operation of the pump, said accumulator-reservoir device including a housing and a sliding piston in said housing in frictional contact with an interior wall thereof, oppositely directed piston portions being exposed to communicate with the system respectively at the suction side of the pump and at the pressure side thereof, said device further including a rolling diaphragm interconnecting said piston and said housing and defining to one side thereof and with a piston portion a chamber in said housing communicating with the fluid system at the pressure side of said pump, said diaphragm being exposed to the other side thereof to the pressure of ambient surroundings, and a spring received in said chamber based on said housing and bearing on said piston, said spring having a force sufficient to overcome frictional resistance to movement of said piston during non-operating conditions of said pump but which force does not significantly affect movements of the piston in an operational mode of the system during which the pump is operating, the spring force applying a minimal fluid pressure maintaining said diaphragm in a normally extended non-inverted convolution during non-operating conditions of said pump.