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Direct operated valves

Direct operated valves

incorporate a temperature sensor inside the valve, and operate independently of external power supplies.

Electrically operated valves

Electrically operated valves

are powered by an external electric actuator, with control provided by a separate electronic control unit, and temperature sensing by resistance thermometer.

Pneumatically operated valves

Pneumatically operated valves

are powered by an external pneumatic actuator, with control provided by a pneumatic controller with external temperature sensing.

Gas operated valves

Gas operated valves

are designed to control refrigerant gas pressures – and hence the temperature of refrigerated or air-conditioned areas – in marine systems in which the condenser is cooled by sea water.

 

Valve Handings

Handing Li

Handing LI

HandingR i

Handing RI

Handing Lb

Handing LB

HandingRb

Handing RB

Handing Lc

Handing LC

Handing Rc

Handing RC

 

 

Electrically operated

The Walton electrically controlled system comprises a 3-way valve with electric actuator, an electronic controller and a platinum resistance thermometer (PRT).

The controller periodically samples the temperature of the coolant system via the PRT and compares this with the predetermined set temperature. If necessary it sends a signal to the valve's actuator to adjust the position of the rotor within the valve. This varies the proportion of coolant passing through the system's cooler to bring the system temperature in line with the set temperature.

The principle advantages of electric over direct operated valves are:

  • Increased flexibility in application
  • In sea water circuits the separation of the main operating mechanism from the circulating fluid will minimise corrosion problems.
  • Increase in power and speed of operation
  • The ability to sense the temperature remote from the valve

Electronically Operated Temperature Control ValveSizes range from 25mm (1") bore to 350mm (14") diameter. The flow rates that these valves can accommodate are shown here.

The valve can be supplied to any one of six possible handings to suit the piping arrangement. These are shown to the left, below.

The system can be supplied to operate at either 220/240V or 110/120V AC 50/60Hz 1 phase.

The 3-way valve body is of the standard Walton type and interchangeable with the bodies used for the range of direct operated valves. This means that it is a simple matter to convert a valve from direct or pneumatic to electric operation, and this can usually be achieved without removing the valve body from the system or modifying the pipework.

Valve description

The valve body has three ports leading into flanged branches. Fluid flow through the valve is controlled by a rotor, the end shutters of which travel over two of the ports to direct flow to either the cooler or bypass branches, or to proportion the flow between the two. The rotor is driven by an electric actuator mounted on the valve; this is activated by a signal from the Walton electronic controller.

Mechanical stops are provided to limit the travel of the actuator (60 degrees) with limit switches set to cut off supply to the motor before either motor or valve stops have been reached. In addition, a stop cast on the valve's front cover provides ultimate protection against the inlet port from being covered by the rotor.

The actuator may be removed from the valve without breaking into the pressure tightness of the system. Alternatively, the actuator, its mounting and the valve's whole internal assembly can be removed without disturbing the valve's pipe connections.

The ability to manually position the valve rotor is provided through a ‘flatted’ shaft protruding through the top cover of the actuator.

The actuator requires a power supply of either 220/240V or 110/120V AC 50/60Hz 1 phase.

Controller description

Electric Valve & ControllerThe function of the Walton electronic controller is to monitor the difference between the system's actual temperature and the desired operating temperature. When necessary, the controller sends instructions to the valve's actuator to adjust the flow of coolant so as to bring the two into line as quickly as possible.

The controller requires an input signal of the system's actual temperature. This is usually generated by a platinum resistance thermometer (PRT) which is installed in the system at the point where the temperature is to be sensed. The PRT converts the temperature into an electrical signal that the controller can recognise. Walton can supply PRTs suitable for most applications. Alternatively, a controller is available which responds to a 4-20mA signal; this can be generated by a wide range of devices.

The Walton electronic controller is available in the following configurations: 

  • Panel mounted This is installed in a control room's main console such that the controller's fascia is incorporated into a larger control system. The electronic parts of the controller are suspended beneath the control panel.
  • Totally enclosed In this design the controller is contained within an aluminium enclosure sealed to IP65. The fascia is accessed by removing the enclosure's cover. This arrangement is suitable for 'dirty' environments such as machinery spaces. Special enclosures are available for protection against sea water and other hostile environments.

The controller's fascia incorporates a facility to set the desired system operating temperature, as well as integral, proportional band and dead zone controls.

The controller requires a power supply of either 220/240V or 110/120V AC 50/60Hz 1 phase.

System design

Diverting or Mixing?

Walton electrically operated valves may be installed as either flow diverting or mixing valves, although the latter is recommended.

When installed as a diverting valve and at temperatures below the set temperature, the rotor directs all the fluid to bypass the cooler, while above the set temperature all the fluid is directed through the cooler. During normal operation the flow is automatically proportioned between the bypass and cooler to maintain the incoming fluid at the set temperature.

When operating in mixing mode, the valve is installed downstream of the cooler. The hot and cold fluid streams enter the valve in a proportion determined by the position of the rotor. The temperature of the fluid leaving the valve is maintained at the set temperature.

Attitude

To mitigate undue loading on the valve mechanism's main bearings, we would recommend that where possible the valve be installed with its actuator in the upright position.

Sampling Interval

The operation of the system requires that the Walton controller periodically samples and compares the temperature in the coolant system with the predetermined set temperature and if necessary adjust the position of the rotor within the valve by means of an electrically driven actuator. The time interval between samples is variable, but to achieve stable control within the system should be as long as possible. It should never be less than the system interval which is the time taken for ‘a given volume of fluid’ to complete the circuit of the system.

Sensor Position

The resistance thermometer generating the operating signal is installed in the system at the point where control of the fluid temperature is required.

Connections

The system pipework should be as simple and compact as possible. The cooler by-pass pipe should be designed for minimal pressure loss. The pressure difference across the 3-way valve at full flow through either the cooler or cooler bypass should not exceed 0.8 bars.

A degree of flexibility in at least one of the connecting pipes is desirable although, if care is taken on installation, not essential. Mounting of the valve should be such that it is not subjected to excessive loading or vibration under running conditions.

For marine applications, temperature variations, pipe expansion and movement of the ship's hull should be taken into account when designing the piping runs and supports.

  
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