Pneumatic Valves

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 self-acting 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.

Description

Valve

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.

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

Controller

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.

Temperature Sensor

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 control of the fluid temperature is required.

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.

Sizes

Walton rotary self-acting valve bore sizes range from 25mm (1.00″) to 300mm (12.00″) diameter.

The maximum flow rates that can be accommodated in each valve size are shown here.

Maximum flow rates in m³/hour

Valve Bore	Fresh Water	Sea Water	Lub. Oil
25mm	10	10	10
40mm	22	16	16
50mm	35	26	26
65mm	60	45	45
80mm	90	67	67
100mm	100	75	75
125mm	160	120	120
150mm	180	180	180
200mm	400	290	290
250mm	600	450	450
300mm	700	520	520

Port configuration

Self acting rotary valves can be supplied in any of six possible port configurations (called handings) to suit your preferred pipework layout. This provides great flexibility – the valve can be supplied to suit the pipework, rather than the pipework having to be adapted to suit the valve.

The possible handings are shown on the right:

System design

Mixing or diverting?

Walton direct operated valves may be installed as either flow diverting or mixing valves.

When installed as a flow diverting valve and at temperatures below the operating range, the rotor directs all the fluid to bypass the cooler, while at temperatures above the operating range, 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 required temperature.

When operating as a mixing valve, the hot and cold fluid streams enter the lower ports in a proportion determined by the position of the rotor and maintain the temperature of the fluid leaving the upper port at the required temperature.

It is recommended that the valve controlling the flow of fluid through or around the cooler is fitted downstream of the cooler to operate as a mixing valve, proportioning the flow between cooler and cooler bypass.

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.

We are always willing to create a customised solution for your application if none of our standard products are suitable

Our advanced computer aided design software and the flexible nature of the Walton valve design mean that this can often be a cost-effective approach.