A twin sensor adaptor, Figure 7.2.7, allows one valve to be operated by a control system with the option of having a manual isolation facility.
The adaptor can be used with both 2-port and 3-port control valves. The advantage offered by the adaptor is that the cost of a separate valve is saved. However, it is not recommended that temperature control and safeguard high limit protection be provided with a common valve, as there is no protection against failure of the valve itself.
A manual adaptor as shown in Figure 7.2.8, is designed to be used with 2-port and 3-port control valves. It can also be used in conjunction with a twin sensor adaptor and a self-acting temperature control system, allowing manual shutdown without interfering with the control settings, as shown in Figure 7.2.7
A spacer (Figure 7.2.9) enables the system to operate at higher temperatures. Each control valve and temperature control system has its own limiting conditions. A spacer, when fitted between the control system and any 2-port or 3-port control valve (except DN80 and DN100 3-port valves), enables the system to operate at a maximum of 350°C, providing that the control valve itself is able to tolerate such high temperatures.
Typical environments and applications
Environments suitable for self-acting temperature controls:
• Any environment where the sophistication of electrical and pneumatic controls is not required.
Especially suited to dirty and hazardous areas.
• Areas remote from any power source.
• For the accurate control of storage or constant load applications, or for variable load applications where high accuracy is not required.
Industries using self-acting temperature controls:
• Milling, heater battery temperature control (non-hazardous).
• Abattoirs - washing down etc.
• Manufacture of oils and fats - storage tank heating.
• Metal plating - tank heating.
• Tank farms - heating.
• Industrial washing.
• Steam and condensate systems.
Heating, ventilation and air conditioning (HVAC)
• Domestic hot water and heating services in nursing homes, hospitals, leisure centres and schools,prisons and in horticulture for frost protection.
The most commonly encountered applications for self-acting temperature controls:
• Boiler feedwater conditioning or direct steam injection heating to boiler feedtank.
• Stand-by generator cooling systems.
• 2-port temperature control and overheat protection, (steam or water).
• 3-port temperature control and overheat protection (water only).
• 2-port time / temperature control (steam only).
• 2-port temperature or time/temperature control and overheat protection (steam or water).
• 3-port control and overheat protection (water only).
Injection (or bleed-in) systems
• 2-port or 3-port injection system.
• Basic mixing valve and compensating control.
• Zoned compensating controls.
• Basic compensator plus internal zone controls.
• Control of overhead radiant strip or radiant panels.
Warm air systems
• Heater battery control via room sensor, air-off sensor or return air sensor.
• Compensating control on air-input unit.
• Low limit and high limit control.
• Frost protection to a heater battery.
Fuel oil control
• Bulk tank heating coil control.
• Control of line heaters.
• Control of steam tracer lines.
• Acid pickling tank.
• Plating vat.
• Process liquor boiling tank.
• Brewing plant detergent tank.
• Drying equipment, for example, laundry cabinet or wool hank dryer, chemical plant drying stove for powder and cake, tannery plant drying oven.
• Continuous or batch process reaction pan.
• Food industry jacketed pan.
• Diesel engine cooling.
• Rotary vane compressor oil cooler control.
• Hydraulic and lubricating oil coolers.
• Cooling control on cold water to single-stage compressor.
• Closed circuit compressor cooling control.
• Air aftercooler control.
• Air cooler battery control.
• Jacketed vessel water cooling control.
• Degreaser cooling water control.
• Control for reducing fireside corrosion and thermal stress in LTHW boilers.
• Hot water cylinder control.
• Temperature limiting.
Applications for the high limit safeguard system
• Preventing temperature overrun on hot water services, or heating calorifiers, in accordance with many Health and Safety Regulations. Good examples include prisons, hospitals and schools. An optional BMS/EMS interface to flag high temperature trip is available.