Caltherm

Oil Cartridge Thermostats

This page is designed to provide a basic understanding of the operation and performance criteria of Caltherm Oil Cartridge Thermostats and to illustrate some of the sizes and styles currently available . If none of the oil cartridge thermostats found on this page fulfill your requirements, Caltherm engineers can custom design a unit for your application.

What is a Oil Cartridge Thermostat?

A Oil Cartridge Thermostat is a thermally actuated valve designed to control the temperature of lubricating or hydraulic oil within a specified range by diverting flow through a heat exchanger. Caltherm Oil Cartridge Thermostats also include a pressure relief feature which allows an override of the thermal actuation.

Where are they used?

Caltherm Oil Cartridge Thermostats are used where optimum system performance is dependent upon controlling oil temperature within a specific range. Typical applications include aircraft engine and hydraulic system coolers, air compressors cooling systems, truck and military vehicle engines and transmission oil coolers.

How are they constructed?

While there is some variation in the design of Caltherm Oil Cartridge Thermostats, depending upon their application requirements, the units exhibit certain basic features as described in Fig 1.

The thermal actuators used in all Caltherm Oil Cartridge Thermostats are of the flat diaphragm type shown in Fig. 2. This insures reliable unit operation even in severe applications involving extremes of temperature, vibration and pressure.

Caltherm Oil Cartridge Thermostat Specifications
The chart below depicts the Caltherm Thermostat specifications of illustrations A-L.

Flow Curve Index    Drawing Index    Photo Index

ALL DIMENSIONS & PERFORMANCE SPECIFICATIONS ARE APPROXIMATE

General Application Questionnaire

Temperature Dependent Operation

The operation of a basic cartridge thermostat of the type shown in Fig 3 is dependent upon a flow restriction differential between the valve port (bypass) and the oil cooler.

When the oil is cool, the valve is open, as in Fig. 3 A. When the flow path through the cooler is more restrictive, the greater oil flow will be through the bypass back to the operating system (engine, compressor, etc.) where it absorbs more heat. As the warmer oil acts on the thermostat, the valve begins to close, creating a restriction through the bypass. This forces more oil to the cooler. At a maximum temperature condition, the valve is fully closed and the total oil flow is through the cooler.

Pressure Override Feature

When the bypass valve is closed, as in Fig. 4 A, the system pressure may increase due to a restriction or blockage in the cooler, or merely as the result of the reduced flow capacity. If this pressure reaches a predetermined level, the bypass spring will allow the valve to "crank" open (see Fig. 4 B), thus overriding the temperature actuation and relieving the pressure build-up.

If you would like additional information on Oil Cartridge Thermostats, or just have questions, please feel free to call or e-mail us at the information below.