How to Prevent Hydraulic Systems from Overheating

By: Brendan Casey
Insider Secrets to Hydraulics (11/03)

Why Do Hydraulic Systems Overheat?

Over-heating of hydraulic fluid in operation is caused by inefficiencies. Inefficiencies result in loss of input power, which are converted to heat. A hydraulic system’s heat load is equal to the total power lost (PL) through inefficiencies and can be expressed as:

PLtotal = PLpump + PLvalves + PLplumbing + PLactuators

If the total input power lost to heat is greater than the heat dissipated, the hydraulic system will eventually overheat.

High temperatures can cause your hydraulic system to overheat

Hydraulic Fluid Temperature – How Hot Is ‘Too Hot’?

Hydraulic fluid temperatures above 180°F (82°C) damage most seal compounds and accelerate degradation of the oil. While the operation of any hydraulic system at temperatures above 180°F should be avoided, fluid temperature is too high when viscosity falls below the optimum value for the hydraulic system’s components. This can occur well below 180°F, depending on the fluid’s viscosity grade.

Maintaining Stable Hydraulic Fluid Temperature

To achieve stable fluid temperature, a hydraulic system’s capacity to dissipate heat must exceed its inherent heat load. For example, a system with continuous input power of 100 kW and an efficiency of 80% needs to be capable of dissipating a heat load of at least 20 kW. It’s important to note that an increase in heat load or a reduction in a hydraulic system’s capacity to dissipate heat will alter the balance between heat load and dissipation.

Returning to the above example, the hydraulic power unit had a continuous power rating of 37 kW and was fitted with an air-blast heat exchanger. The exchanger was capable of dissipating 10 kW of heat under ambient conditions or 27% of available input power (10/37 x 100 = 27). This is adequate from a design perspective. The performance of all cooling circuit components were operating within design limits.

Pressure Drop Means Heat

At this point it was clear that the overheating problem was being caused by excessive heat load. Concerned about the length of the umbilical, I calculated its pressure drop. The theoretical pressure drop across 710 feet of ¾” pressure hose at 24 gpm is 800 psi. The pressure drop across the same length of 1″ return hose is 200 psi. The formula for these calculations is available here. The theoretical heat load produced by the pressure drop across the umbilical of 1,000 psi (800 + 200 = 1000) was 10.35 kW. The formula for this calculation is available here.

This meant that the heat load of the umbilical was 0.35 kW more than the heat dissipation capacity of the hydraulic system’s heat exchanger. This, when combined with the system’s normal heat load (inefficiencies) was causing the hydraulic system to overheat.

Beat The Heat

There are two ways to solve overheating problems in hydraulic systems:

1. Decrease heat load

OR

2. Increase heat dissipation.

Decreasing heat load is always the preferred option because it increases the efficiency of the hydraulic system. In the above example, the heat load of the umbilical alone was nearly 30% of available input power, a figure that would normally be considered unacceptable. Decreasing this heat load to an acceptable level would have involved reducing the pressure drop, by replacing the pressure and return lines in the umbilical with larger diameter hoses. The cost of doing this for what was a temporary installation meant that, in this case, the most economical solution was to install additional cooling capacity in the circuit.

Continuing to operate a hydraulic system when the fluid is over-temperature is similar to operating an internal combustion engine with high coolant temperature. Damage is guaranteed. Therefore, whenever a hydraulic system starts to overheat, shut it down, identify the cause and fix it.

This entry was posted in Tips & Tricks and tagged , . Bookmark the permalink.

6 Responses to How to Prevent Hydraulic Systems from Overheating

  1. I’m not sure why but this weblog is loading very slow for me. Is anyone else having this issue or is it a issue on my end? I’ll check back later on and see if the problem still exists.|
    fake cartier yellow gold love bracelet [url=http://www.whatjewelleryhouse.com/]fake cartier yellow gold love bracelet[/url]

  2. your video says:

    Hello
    Dean here from Kent, I was just looking at your site and just wanted to ask you a quick questions
    how many new sales do you think you would gain if you had a video commercial on the front page of google for EVERY search term related to to your service or product??
    yep! a video commercial showing for every possible term people could type into google to find what you sell or the service you provide…
    sound to good to be true?
    take a look at this video and case study I am sure you will be blown away by the results
    this works if you sell products online or run a service in a local area.
    http://allhatsseo2u.com

  3. Sammy Waner says:

    I got what you intend,bookmarked, very nice internet site.

  4. Krista says:

    Hey very cool site!! Man .. Beautiful .. Amazing .. I will bookmark your blog and take the feeds also…I’m happy to find so many useful information here in the post, we need work out more techniques in this regard, thanks for sharing. . . . . .

  5. 42535 282085Also, weblog often and with fascinating material to keep individuals interested in coming back and checking for updates. 896324

  6. Shantay says:

    Thank you for the auspicious writeup. It in fact was a amusement account it. Look advanced to more added agreeable from you! By the way, how can we communicate?

Leave a Reply

Your email address will not be published.

Price Engineering Company, Inc. BBB Business Review