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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

 

 

Pneumatically Operated

The Walton pneumatically controlled system comprises a 3-way valve with pneumatic actuator and an independently located pneumatic controller incorporating an internal or external temperature sensor.

The controller samples the temperature of the system and compares this with the predetermined set temperature. If necessary it varies the air pressure 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 pneumatic 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.

Pneumatically Operated temperature Cotrol ValveSizes range from 40mm (1.5") 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.

Provision for manual operation is a standard feature of the Walton pneumatically operated valve.

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 to pneumatic operation, and this can usually be achieved without removing the valve body from the system or modifying the pipework.

The pneumatic controllers available are:

  • Proportional only (‘P’) Reverse Action Pressure Controller fitted with a wax filled type sensor as used in the direct operated valves. A supply of clean, dry air at 3-7 bar is required.
  • Proportional and Integral (‘P+I’) Mercury in steel sensor housed in stainless steel pocket and connected to the controller measuring unit by a capillary tube. A supply of clean, dry air at 1.38 bars is required.
  • Proportional, Integral and Derivative (‘P+I+D’) This system may use a controller having an electro-mechanical transducer which converts an electric input signal of 4-20 mA or 0-20 mA; 1-5V Dc or RT 100 resistance to a pneumatic signal which is then relayed to the valve actuator.

System design

Diverting or Mixing?

Walton pneumatically 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.

Sensor Position

The sensor generating the operating signal is mounted 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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