Motorised Valves

From DIYWiki
Revision as of 00:20, 21 July 2007 by (talk)
Jump to navigation Jump to search

free motorola ringtones buy soma free motorola ringtones tramadol online cyclobenzaprine online cheap norco cheap celexa cyclobenzaprine online ultram online propecia online cheap celexa verizon ringtones cheap xenical cheap ambien cheap albuterol cheap ultram cheap ultram buy tramadol ambien online cheap carisoprodol free mp3 ringtones norco buy vicodin sony ringtones buy hoodia cheap sildenafil cheap vicodin free motorola ringtones free jazz ringtones qwest ringtones cialis online ambien online lisinopril online free verizon ringtones cheap valium cheap ultram buy meridia levitra online xenical online free cool ringtones ortho online cheap xanax online fioricet but fioricet free nokia ringtones lipitor mono ringtones buy diethylpropion free sharp ringtones jazz ringtones cheap diethylpropion phentermine online cheap hydrocodone sharp ringtones free sony ericsson ringtones cool ringtones cheap flexeril cheap didrex nextel ringtones zyban online free ericsson ringtones cheap hoodia tracfone ringtones cool ringtones music ringtones but clonazepam didrex online ultracet online celexa online flexeril online sagem ringtones free tracfone ringtones order zyban lortab online ultracet online lorazepam online zoloft nexium online cheap xenical free nokia ringtones free mono ringtones nextel ringtones free motorola ringtones cheap lortab diazepam online free qwest ringtones tramadol online cheap levitra clomid online levitra online free sprint ringtones punk ringtones prozac online nexium online cheap lortab flexeril ambien online free funny ringtones hgh online polyphonic ringtones buy diethylpropion adipex online free sony ericsson ringtones ativan online free sagem ringtones cheap meridia online flexeril cheap clonazepam buy flexeril ultracet online buy diethylpropion mtv ringtones real ringtones albuterol online cheap xanax cheap lisinopril ultram online alprazolam online jazz ringtones free sprint ringtones fioricet online alltel ringtones free nextel ringtones prozac online online zyban hydrocodone online xenical online vicodin soma online buy tenuate free motorola ringtones free polyphonic ringtones ortho albuterol online prozac online but clonazepam funny ringtones nextel ringtones samsung ringtones free tracfone ringtones hgh online xenical online cheap fioricet wellbutrin online cheap lipitor order viagra cheap valium zanaflex online free sprint ringtones free nokia ringtones polyphonic ringtones nokia ringtones kyocera ringtones didrex free cingular ringtones valium online free qwest ringtones carisoprodol online sprint ringtones sharp ringtones cyclobenzaprine online tenuate online diethylpropion online order rivotril free sagem ringtones buy ultram free mono ringtones buy tenuate samsung ringtones buy rivotril free nextel ringtones clomid online buy ativan tramadol online didrex online sprint ringtones cheap ultracet tramadol online propecia online sharp ringtones tenuate buy tramadol real ringtones free nokia ringtones cialis online ativan online cingular ringtones buy ultram viagra online clonazepam online order viagra free sprint ringtones cheap zoloft cheap zanaflex buy carisoprodol nokia ringtones free sony ericsson ringtones cheap ultracet samsung ringtones zoloft This article is about motorised valves used in Central Heating systems. Motorised valves are a type of electrically actuated valve (others include solenoid valves and valves using electrically-generated thermal effects).

Motorised valves generally comprise:

  • a synchronous electric motor
  • gears to reduce the speed and increase the torque output of the motor

The motor and gears are often combined in a package known as a Synchron motor.

  • a linkage from the output gear to the hydronic part of the valve
  • one or more switches (usually microswitches) actuated by, for example, 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:


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.


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.

Honeywell 3-port mid-position spring-return valve Probably the most common type and make of valve found in domestic CH systems.

There are two types 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 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 radiator circuits in a Y-plan system configuration.

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.

These types of valve consume power whenever they are open (and, in the case of 3-port valves, often even when they are not). In 2-port valves the motor runs until the valve is fully open and then stalls as the actuator mechanism cannot move any further. 3-port valves are more complicated: a description can be found in the uk.d-i-y FAQ and here is a diagram showing a 3-port valve in a Y-plan CH system

Motor open/motor close valves

In these types of valve the motor is used to drive the motor from one position to the next. Switches in the mechanism stop the motor when it has reached its desired position.


This type of valve changes from it closed to its open position when power is applied to one terminal, and from open to closed when power is applied to another terminal.

                   ENERGISE                ENERGISE
                   TO CLOSE                TO  OPEN
                       |                       |
                     white                   yellow
                       |                       |
                       o                       o
                       /                       /
                     o/   o                  o/   o------- orange ----> TO BOILER
                     |                       |
                     |                       |
                      ----------- -----------
                             |       |
                             | MOTOR |
                             |       |
         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.)

If a motor-open/motor-close valve is replaced by a spring-return valve, or vice-versa, the controls wiring must be modified to suit. In the case of replacing a spring-return with a motor-open/motor-close valve this requires change-over contacts at the room thermostat (or progstat) and an extra wiring conductor between the 'stat and the valve.

This type of valve is also found in non-domestic installations.
Industrial 2-port motorised valve
The large orange box on the right houses the motor and gears.
The smaller orange box on the left contains the switches.


Sunvic's SDMV series 3-port valves are motor-open/motor-close types but are wired identically to spring-return valves.

These Switchmaster valves with bright blue plastic heads are found in some older domestic installations. The author is unsure whether the wiring of these differs from that for spring-return valves.
CH motorised valve Switchmaster 3-port mid-pos (end).jpg CH motorised valve Switchmaster 3-port mid-pos (top).jpg CH motorised valve Switchmaster 3-port mid-pos (inside).jpg