Coping with Specialty Fluids for Hydraulic Testing #5: Cold Fluid Temperature Testing

This is the fifth in a series of articles outlining the system requirements and considerations when using specialty fluids for product test stands. This issue is the last in this series and will address Low Temperature Testing considerations.


Figure 1- A WTI Temperature Test System
Figure 1- A Genuen Temperature Test System

Temperature Testing

One of the most stringent types of Servo Hydraulic Fluid Testing is high- and low- temperature testing. Some of our customers, and even many of our competitors, have fallen into the troublesome task of designing and building a test system to test at either a high temperature or a low temperature. And even more difficult testing is temperature sweep testing, from ambient to low, to high, and then back to ambient. These tests can be “one-off” to test a product’s reaction to a temperature, or multiple sweep tests, and can continue for many hours or even weeks. Anyone who has applied this type of testing clearly understands that simply raising or lowering the fluid temperature is not the solution to the testing, but the cause of the application problems.

Low-Temperature Testing

Testing at low temperatures can create many problems in the design and build of a test system. Some key areas for consideration are:

Thermometer 2Test Temperatures – Most of today’s cold fluid testing generally ranges from ambient to -40°F (-40°C), although in recent months the requested temperatures are trending to as low as -61.6°F (-52°C). Fluid temperatures can be varied in a simple stepped test, with several increasing/decreasing temperature points, or as is the more complicated sweeping temperature test, from high to low and back to high, with very specific linear data points to achieve.

Test Fluids – Test fluid can range from many variations of oil, transmission fluid, or any fluid associated with a part’s operation.

Methods of Testing – The method and type of system required to perform cold fluid testing is generally determined by the target test temperatures. While the following test temperature ranges are “base rules of thumb,” each test case should be reviewed for flow, input horsepower (heat), ambient temperatures, length of runs, and part accessibility.

o Ambient to 0°F (-17.7°C) testing


Figure 2 Environmental chambers can be supplied in many types and sizes to suit a specific application. Figure 2 - Environmental chambers can be supplied in many types and sizes to suit a specific application.

Testing with fluid temperatures down to 0°F (-17.7°C) can normally be accomplished through the use of fluid chillers, insulation of the part, and control components, lower operating flows, and close proximity of the fluid source/conditioner and the test part.

o Ambient to -20°F (-28.9°C) testing

WTI normally recommends that any testing under 0°F (-17.7°C) be conducted in a thermal chamber or within an insulated enclosure. This can range from a walk-in room, stand-alone or benchtop chamber, to a removable, insulated hood or clam shell cover. Again, all of the conditions as listed above still apply and should be weighed against the actual ambient temperature being maintained.


Figure 3 – The formation of Ice can be quite dramatic if the test chamber is exposed to ambient temperatures during a test. Figure 3 – The formation of Ice can be quite dramatic if the test chamber is exposed to ambient temperatures during a test.

o Ambient to -40°F (-40°C) or below testing

The requirements of testing to very low temperatures requires too many design issues to be addressed within this article. Consideration of integrating the fluid power control components into the chamber, locating the fluid within the chamber, additional fluid condition units, eliminating or reducing induced heat in the test system, and test temperature profiles all come into play within these systems. Rely only on system integrators who are experienced in very cold testing applications when developing a test system; cold temperature testing relies heavily on a “lessons learned” history and can save you a tremendous amount of development time and funding.

Potential of Injury to Personnel – Additional guarding, interlocked guard doors, and redundant safeties are a must when developing a cold test system. The protection against frostbite, inhalation hazards (if using an inert gas to speed-up temperature swings), and water (ice) build-up reduction should also be taken into consideration when developing a system.

Component Selection – Plain and simple, fluid power components do not react the same when operating at cold temperatures as they do at their -100°F (-37.7°C) rated temperatures. Component selection must include consideration of the fluid viscosity at the test temperature, the type of seals and materials, rated component flows and leakages, and component life/warranties.

Other Requirements

Other designed and operational requirements which must be taken into consideration include:

Mass loads of fixtures and parts – Getting the fluid cold is only one portion of the test. Additional capacities must be included for cooling of fluid, components, the mass of the test part(s), and the surrounding environment. These must also be considered during the design phase of the project.

Heat Transfer – One seldom-considered effect of low-temperature systems is the transfer of heat into the test environment. Designing a system to reject ambient temperature(s) and to compensate for the injected heat being generated within the test part itself, is a big part of designing a system.

Maintenance of the fluid – The fluid’s condition must be constantly monitored for chemical reactions due to the low test temperatures. In addition, regular water analysis and removal should be provided to reduce possible component failures.

Genuen (formerly Wineman Technology) has proven experience with all types of temperature testing to suit all of your applications. To avoid the pitfalls of cold fluid testing, rely on us for all of your temperature test system’s needs. For more information on please contact Genuen today.


Read the first blog in this series here.


About Genuen

Our goal is to improve time to market without compromising product quality or safety standards. With experience in mission-critical applications and regulatory compliance, Genuen creates custom test systems across the product lifecycle, including hardware-in-the-loop (HIL), fluid power test, and electromechanical test. Headquartered near Kansas City, we have offices across the United States and serve clients in aerospace, transportation, national security, and beyond. The company's Quality Management System (QMS) is certified to ISO 9001.