Patent GB-1363736-A (GB)
Title: Fluid pressure boosters
IPC: G05D16/20
Filed: 1971-10-21
Abstract: 1363736 Automatic control of pressure POMPES ESSO-MICO SA 21 Oct 1971 [22 Oct 1970] 49058/71 Heading G3R [Also in Divisions F1 and H2] A fluid distribution circuit includes a fluid source, a variable fluid consuming load, at least two booster pumps connected in parallel, one of the pumps being a rotary pump providing when rotated in one direction a reduced flow in the same direction as a greater flow provided by rotation in the opposite direction, and means for controlling the direction of rotation of this pump to compensate for decreasing fluidpressure in the circuit arising from an increasing consumption by the load. The pressure of the water supply of a block of flats is variably boosted, to cope with variable demand, by means of two identical centrifugal pumps PA, PB driven by reversible three-phase electric motors, each pump having a reduced performance when driven in the reverse direction. In Fig. 1, which is a graph of pressure against flow, the horizontal line N represents the pressure before boosting, while T is an ideal curve of pressure after boosting, the actual curve after boosting being the saw-toothed line shown. Either of the two pumps can be selected as the priority pump. When switch 53, Fig. 2a, is in the position shown, it energizes a relay R 2 , Fig. 2b, to give priority to pump PB. When switch 53 is in the opposite position, it energizes a relay R 1  to give priority to pump PA. In both cases, a relay R 3  is also energized. Assuming that PA is the priority pump, a relay PPA(-) is energized via the relays R 1  and R 3  to switch the motor MA of pump PA into reverse rotation so that pump PA operates on curve PA(-) to cope with low demand. If the demand increases to such an extent that  the pressure falls to the value M, a pressuresensitive switch MO closes to energize a relay RA M O  which in turn energizes a time lag relay RT 1 , the contacts 7, 29 of which remain closed for about 1¢ minutes after the pressure ceases to be below the value M. This produces ener-  gization of a relay RPB(-) during this period, whereby the motor MB of pump PB is operated in reverse direction. Both pumps are now running in reverse direction and in parallel with one another to operate on a curve PA(-) + PB(-). At the end of the period, pump PB is stopped and pump PA operates alone on the curve PA(-) unless the pressure is then still below the value M. If during the above-mentioned period the pressure falls to the value P, a pressure-sensitive switch PR 1  closes to energize, after a predetermined interval, a time lag relay RT 2  which in turn de-energizes relay R 3  to cause de-energization of relays PA(-) and PB(-) and the consequential energization of a relay RPA(+) which then switches the motor MA to drive the pump PA in the forward direction so that it operates alone on the curve PA(+). Operation on this curve continues as long as the pressure remains between the values Q and R. If the pressure rises above the value Q, the pumps revert to operation on the curve PA(-) + PB(-) at the end of the time delay imposed by the relay RT 2 . If, however, the pressure drops to the value R, a pressure-sensitive switch PR 2  closes to energize, after an interval, a time-lag relay RT 3  which in turn energizes a relay RPB(+) to cause motor MB to drive the pump PB in the forward direction. The two pumps then operate in parallel along the curve PA(+) + PB(+). If the pressure then rises above the value S, the pump PB will be stopped at the end of the time delay (e.g. 1¢ minutes) imposed by the relay RT 3 , and operation then reverts to the PA(+) curve.