Standard pilot-operated globe control valves are often specified for level control. But, they are not suitable in some installations:-
- In low pressure installations (below 1.5 bar dynamic pressure).
- When dirt particles in the water might clog small orifices.
- Where they might be subject to vandalism.
A diaphragm valve offers several advantages in these cases:-
- They have a wide range of operating pressures. 0.05 bar (0.5m head) to 6 bar inlet pressure is typical. Including a ratio reducing valve upstream allows for higher inlet pressure if needed.
- They are available in sizes from 100mm to 1600mm.
- They can be installed inside the reservoir, below water level, which reduces the risk of vandalism.
- They can be fabricated to suit reservoir piping configuration. This reduces the cost when retro-fitting to existing pipework.
- They are installed and commissioned by the factory team.
The diagram below shows how a diaphragm valve works when used for reservoir inlet control.
The desired level is set at the sensing element. This can be adjusted as shown in the diagram. When water enters the sensing element the head of water charges the diaphragm. This causes the valve to close.
Diaphragm valves can face up or down. This makes them very versatile and other uses include:-
- Canal flow regulation for raw water in irrigation schemes.
- Discharges into holding or balancing dams in irrigation schemes. The diaphragm valve controls the inflow as well as closing when the dam is full.
- Flow control into raw water and wastewater treatment works.
- Reservoir top and bottom inlets.
- Bottom outlets from dams.( The diaphragm valve has very good energy dissipation characteristics.)
- Actuation and control for automatic spillway scour and canal gates.
Diaphragm valves need no maintenance, which makes them suited for remote sites and our sometimes harsh African conditions.
Flow can be controlled automatically as described in the reservoir example above. Bu,t they can also be fitted with a small electric actuator and connected by telemetry to allow remote adjustment.