Motorised Valves

This article is about motorised valves used in Central Heating systems. Motorised valves are one type of electrically actuated valve, others including solenoid valves and valves in which electrically-generated thermal effects are used.

Motorised valves generally comprise:

• a synchronous electric motor
• gears to reduce the speed and increase the torque output of the motor
• a linkage from the output gear to the hydronic part of the valve
• one or more switches (usually microswitches) actuated by, typically, a cam attached to the output linkage
• a spring: see below

the above components usually comprise one module, often known as the 'head', which may be detatched from the parts below for repair or replacement.

• a valve controlling flow of water in the hydronic system, actuated by the head: this part is often known as the 'body'.

Configurations of motorised valve

Valves are commonly found in the following configurations:

2-port

The valve has 2 pipe connections (ports) and permits or blocks flow between the ports depending on whether it is actuated or not. Flow is permitted when the valve is actuated and blocked in its resting state.

3-port

The valve has 3 pipe connections, in a 'T' formation. The centre leg of the 'T' is the inlet and the two short arms are the outlets, usually referred to as ports A and B. Actuation controls whether the flow from the inlet passes to the A or B port. In the resting state flow is to the A port.

There are two variants of 3-port valve:

Diverter valve

This is a simple change-over version of a 2-port valve: when the valve is actuated all flow is diverted to the other (usually B) outlet.

Mid-position valve

In this type of valve there is a stable state in which flow from the inlet can pass to both (A and B) outlet ports simultaneously. This type of valve is commonly found in domestic central heating systems where it controls flow of hot water from a boiler to hot water and space radiator circuits.

Types of motorised valve

Spring return valves

In these types when power is applied the motor and gears act against the force of a spring to operate the valve. When power is removed the spring returns the valve to its resting position. In a 2-port valve this is the closed position. In a 3-port valve the resting position is where flow from the inlet passes to the A port.

Non-spring type valves

2-port

In these valves the motor and gears operating the valve continue to rotate in the same direction to move the valve from closed to open and back again. Two switches are arranged so that one switch operates when the valve reaches the open position and the other operates when the valve reaches its closed position. Actuation of the valve is by applying power to the motor via either of these switches.

                   ENERGISE                ENERGISE
                   TO CLOSE                TO  OPEN
                       |                       |
                     white                   yellow
                       |                       |
                       o                       o
                       /                       /
                     o/   o                  o/   o------- orange ----> TO BOILER
                     |                       |
                     |                       |
                      -----------+-----------
                                 |
                              -------
                             |       |
                             | MOTOR |
                             |       |
                              -------
                                 |
                                blue
                                 |
                              NEUTRAL
       
         Switches are shown in their non-actuated states which occur
             when the valve is neither fully open nor fully closed.
         The switch on the left operates when the valve reaches its closed position.
         The switch on the right operates when the valve reaches its open position.

These types of valves are occasionally found in domestic central heating systems: usually as Satchwell or Sunvic valves with grey plastic heads. (Note however that Sunvic also make almost identical spring-return valves.)

This type of valve is also found in non-domestic installations.

 
 The large orange box on the right houses the motor and gears.
 The smaller orange box on the left contains the switches.

3-port

Occasionally non-spring type 3-port valves are found in older domestic installations; usually as Switchmaster valves with bright blue plastic heads.