GB1138895A - Minimum amount control for centrifugal type boiler feed pumps - Google Patents

Abstract

1,138,895. Centrifugal pumps. W. ODENDAHL. Aug. 10, 1966 [Aug. 30, 1965], No. 35716/66. Heading F1C. A centrifugal boiler feed pump 2, Fig.2, delivers feed water from a reservoir 14 to a boiler 9 via a check valve 16 and a feed regulating valve 5, overheating of the pump during low-load or noload operation being prevented by a by-pass valve 11 which opens to ensure a minimum circulation through the pump, via a connection 10 and a return pipe 12. The by-pass valve 11 is opened by a piston 19 which lifts the valve stem 27, the piston being controlled via a pipe 18 by a control valve 17 comprising control ports 26 formed on the stem 15 of the check valve 16. When the feed regulating valve 5 is closed, and the resultant cessation of flow causes the check valve 16 to close, the valve 17 is opened to allow water to pass via pipe 18 to lift the piston 19, thereby opening the by-pass valve 11. The water acting on the underside of the piston 19 leaks around the piston and then passes via a throttle needle 28 carried by the piston to a pipe 20 containing a check valve 21 and connected to the main circuit at a point downstream of the feed regulating valve 5. The increase in the pressure above the piston 19 produced by the throttle needle 28 as the piston is lifted reduces the net lifting force. The resultant progressive operation of the by-pass valve 11 controls the by-pass flow in accordance with the feed flow to the boiler in such a manner that the sum of the two flows remains constant in the low-load range. This effect can also be obtained by omitting the throttle needle 28 and providing a spring on the valve stem 27 to oppose the lifting of the valve 11. The pipes 18, 20 may be inter-connected by a pipe 22 containing a throttle valve 23. A valve head (30), Fig. 3 (not shown), may be provided at the lower end of the valve stem (15) to co-operate with a bore (31) to provide an additional throttling effect in series with the throttling effect of the ports (26), the arrangement being such that the additional throttling effect is at a maximum in the mid-lift range. The resultant increase in the pressure gradient acting on the stem (15) increases the closing force exerted on the check valve (16) in the partial-load range, whereby a steeper variation of net pumping head with the feed flow is obtained. This facilitates the feed regulation and the operation of two pumps in parallel. In a modification, Fig. 4 (not shown), the control valve 17 is replaced by a rotary control valve (32) connected in series with the connection (10).