Pressure Reducing
details:
The downstream pressure is held constant under varying supply pressure and demand. The pressure reducing pilot senses the downstream pressure and regulates the main control valve accordingly.
Reduction in demand, or increase in supply pressure will increase the pressure into a system. The pilot senses the changes in the system pressure, and will close the main valve more which supplies the new demand at the constant set pressure.
Increase in demand, or drop in supply pressure will reduce the pressure into the system. The pilot senses the drop in system pressure, and opens the main valve further to supply the demand under the changed conditions at the constant set pressure.
Pressure Sustaining / Relief
details:
The Pressure Sustaining function positions the valve to maintain a minimum supply (upstream) pressure into the valve.
The pilot senses the supply pressure and opens on the supply pressure reaching the pilot setting. The main valve then opens and supply demand into the system.
Should the supply pressure tend to fall to the pilot setting, the pilot will close the main valve partially, maintaining a constant supply pressure.
For the Pressure Relief function, the pilot setting is higher than the system setting, but within the safety pressure for the system.
Should the system pressure rise, the pilot opens the main valve, relieving the pressure. Speed controls are fitted, to allow the valve to open instantaneously and to close slowly to prevent any pressure surges.
Level Control
details:
The main valve is controlled by a float pilot in a reservoir. There are two types of float pilot valves; Maintain high level in a reservoir (Modulating) or Open and Closed within a level difference of 1m (On/Off)
On reaching a low level, the pilot is opened and drains the valve control chamber allowing the main valve to open and fill the reservoir.
The main valve opens fully and is sized to admit more water into the reservoir than the demand from the reservoir.
On reaching the high level, the pilot closes and the main valve control chamber is pressurised. The main valve closes, shutting off the supply into the reservoir.
Solenoid Valve
details:
The solenoid valve either opens or closes the main control valve, by means of an electrical solenoid.
The valve can be open or closed, by energising or de-energising a solenoid valve. Water pressure is either pressurising or draining the control chamber of the control the valve. A solenoid valve will either open fully or close drip tight.
The solenoid control valve can be used with other functions like pressure reducing and pressure sustaining. This is used in automation of plants, where an electrical signal is given to a valve to open or close, adding the function of pressure or flow control either up or down stream.
Pump Control
details:
The pump control valve eliminates pressure surges during starting and stopping of pumps. It does automatically, what plant operators do manually.
The valve is in the closed position when the pump starts. The valve will open gradually, slowly increasing the line pressure to full pumping head.
A limit switch connected to the valve position indicator will give an open signal.
On stopping of the pump, a signal is sent to the control valve with the pump still running. The valve will close gradually till in the closed position, where the close limit will stop the pump motor. This prevents any surges during pump stopping.
In the case of power failure or unexpected pump stop, the pump control valve will close, acting as a non return valve, preventing reverse flow and rotation of the pump.
Altitude Control
details:
In this system, the water level in a reservoir can be controlled from 6 meters up to an altitude of 45 meters above the control valve.
The valve is controlled by an altitude pilot valve that senses the change in head of the water through a sensing line. The pilot valve controls an accelerator valve which in return controls the main valve.
During times the supply line is not pressurised, the valve will act as a non return valve, preventing the drainage of the reservoir back into the supply line.
On reaching a high level in the reservoir, the pilot pressurise the main valve control chamber, closing the valve.
On a drop in water level, the pilot drain water from the main valve control chamber, opening the valve.