The particular advantage of the Walton direct operated valve is that it operates independently of external power supplies. It is therefore 'fit and forget'.
The valve contains a control mechanism within it which proportions the system's flow between the cooler and a bypass, thereby maintaining a constant temperature. This mechanism is powered by a thermostatic element which expands at a pre-set temperature, creating the necessary movement.
The temperature range of each valve is fixed during manufacture and can only be altered by replacing its thermostatic element for one designed to operate within a different range. The standard temperature ranges are:
| ºC |
ºF |
| 10/18 |
50/64 |
| 14/26 |
57/79 |
| 20/30 |
68/86 |
| 27/40 |
80/104 |
| 31/42 |
88/108 |
| 37/47 |
99/117 |
| 40/50 |
104/122 |
| 43/54 |
110/130 |
| 51/60 |
124/140 |
| 57/66 |
135/150 |
| 63/71 |
145/160 |
| 68/78 |
145/160 |
| 74/82 |
165/180 |
| 79/88 |
175/190 |
| 85/93 |
185/200 |
| 86/99 |
187/210 |
The temperature that each valve maintains in operation can be set during manufacture so that in practice any temperature between 20ºC and 95ºC can be controlled by selecting the most suitable thermostatic element and adjusting the control point as necessary.
An external lever allows the automatic mechanism to be overridden and the temperature to be controlled manually. The ability to control manually at a temperature lower than that being automatically maintained is of particular value when an individual section of the system is running ‘hot’, or in the unlikely event of an element failure.
Sizes range from 25mm (1.0") bore to 250mm (10") 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.
System design
Diverting or Mixing?
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 within the range of the temperature sensitive element with which the valve is fitted. 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 within the operating range of the element.
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
The valve may be installed in any attitude, gravity having no effect on its operation.
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.