The AR Valve of our SSV series 18, 19 and 20 is a reliable device that automatically protects centrifugal pumps against wear, total loss and damage that can result from running dry, from cavitation or from operating under low-load conditions, generally suitable for pressures up to 140 bar (SSV18) or up to 180 bar (SSV19). As soon as the main flow falls below the required minimum flow, the valve opens its bypass to the extent that the required pump minimum flow is discharged even if the main flow is zero. The pressure in the bypass is reduced via an inte­grated throttle line with a bypass non-return valve. The SSV series 10, 11 and 12 work with pressure reduction in the bypass by throttles only.

Scope

The most relevant application for this valve type is the boiler feed water cycle of combined cycle power plants (CCPP). In these power plants the bfw-pumps operate frequently at minimum flow conditions with pressures of 100–250 bar. The reason is the technical concept of a CCPP – for example gas turbine cooling with bfw – as well as its purpose to cover load peaks or the natural load fluctuation of renewables in the energy grid.

Good to know: the SIP30 model is focused on the replacement of competitor valves with similar bypass technology in terms of the pressure reducing piston. That means, we have the solution to copy the main valve dimensions (S, L, H) so that a 1:1 replacement without adaptions can be achieved when replacing.
Remains to be mentioned that the SIP series has significant technological advantages that make the difference after all. Available to explain further on.

Operating principle

The bypass of the SIP valve is controlled by a multistage piston providing a near cavitation-free operation at any time thanks to the multistage pressure reduction at all flow rates. The piston also ensures a modulating flow control from 100 %–10 % bypass flow rate. An accelerated shut-off (1–2 sec.) at <10 % opening avoids most wear critical operation range. The wear-intensive extreme partial load range is deliberately overridden. The piston seat is separated from the pressure reduction and located at the high-pressure side. Thus, the shut-off function is optimally protected against cavitation attack. Even if cavitation would occur in the last throttle stages, the shut-off function would not be affected leaving the valve fully functional.

Scope

Generally, the SHP valve applies to similar fields of services as the SIP type. Applications with frequent plant operation at minimum flow conditions with partially open bypass, i. e. split flow to process and bypass line. But due to its pilot operated powerful actuating system it is not restricted to discharge pressures below 250 bar. It can easily handle discharge pressures above 400 bar. Thus, it is also suitable for related injection services in the offshore market or high efficiency coal fired plants.

Operating principle

The bypass of the SHP valve is controlled by a multistage piston providing a near cavitation-free operation at any time thanks to the multi­stage pressure reduction at all flow rates. The piston also ensures a modulating flow control from 100 %–10 % bypass flow rate. An accelerated shut-off (1–2 sec.) at <10 % opening avoids most wear critical operation range. The wear-intensive extreme partial load range is deliberately overridden. The piston seat is separated from the pressure reduction and located at the high-pressure side. Thus, the shut-off function is optimally protected against cavitation attack. Even if cavitation would occur in the last throttle stages, the shut-off function would not be affected leaving the valve fully functional.

Scope

The properties of the SMA automatic minimum flow system make it the ideal valve for the protection of pumps in steel mills (descaling applica­tions), but also for power plants or in­jection service in on-/offshore applications.

Operating principle

The SMA valve is equipped with an ON/OFF function: The recirculation flow is controlled by means of a piston, which is either in fully open or fully closed position. This ON/OFF-characteristic of the bypass has a switching time of max. 2 seconds. The pressure breakdown in the bypass is done by a multistage throttling system. As soon as the main pump flow falls below a predetermined value, the valve opens the bypass and safely drains the minimum volume, even if the pumping volume in the main flow direction drops to zero. The bypass is always completely opened or closed through its pilot-controlled valve piston. This ON/OFF control makes it possible to increase the previous load limit of the valves from 200 bar to > 400 bar discharge pressure. The preferred utilization range is thus between PN 250 and PN 400 or ANSI CLASS 2500. The bypass amount may be up to 35 % of the main pumping volume.