Saturday, 28 February 2015

CAUSES OF HYDRAULIC SYSTEM OVERHEATING

CAUSES OF HYDRAULIC SYSTEM OVERHEATING

As we have discussed in previous post “True cost of hydraulic oil” that we are using considerably hydraulic unit these days in various industries for different activities and we have studied the real cost of hydraulic oil leaks.

Why we are going to read this post???

After reading this post we will have information about the overheating of hydraulic system and we will also discuss the solution for each issue.

Hence, let us come to the main subject.

Why do hydraulic unit overheat?

Inefficiencies are the basic reason behind the heating of hydraulic oil during the operation of hydraulic unit. Due to these inefficiencies, there will be lost in input power and this lost in power will be converted in terms of heat energy and will be named as system’s heat load.

Heat load of a hydraulic system will be equal to the total power lost in system due to inefficiencies during operation. We may write one simple equation to understand the total power lost during operation as mentioned below

Total power loss = Power loss in pump + Power loss in valves + power loss in piping + power loss in actuators 

In order to make heat balance, we use heat dissipation device such as heat exchanger or coolers but we must note that if still we are facing problems of heating of hydraulic fluid then in that situation we may easily conclude that heat load i.e. total power lost in system will be larger as compared to heat dissipation.

Now one question is normally asked, how much higher fluid will be considered as overheated hydraulic unit?

If hydraulic fluid temperatures are beyond the 820C, it will surely damage the o ring, main pressure seals; back up seals and other sealing accessories as well as this much heat would also be the prime reason of degradation hydraulic oil.

We must avoid operating the hydraulic system if hydraulic oil temperature is beyond 820C. If viscosity of oil falls below the optimum value then temperature of hydraulic oil will be increased.

What we should do to maintain the temperature of hydraulic fluid?

In order to maintain the required temperature, hydraulic system should have facility to dissipate the heat. Let us consider one example, we have one hydraulic system and input power is 125 KW and with efficiency of 85 %, or we may say that system inefficiencies is 15 % , so how much heat load will be there in our hydraulic system.
Heat load will be 125*15/100 KW or 18.75 KW; hence we must have to use one heat exchanger or oil cooler with capacity of removing heat load of minimum 18.75 KW.

Let us understand the heat load, Heat load is basically defined as the required value of heat that should be removed from a system in a specified time.

We must assure that there should be balance between heat dissipation and heat load. If heat exchanger effectiveness will be reduced, heat load could not be dissipated completely and hence temperature of hydraulic oil will be increased. 

If efficiency of system will be reduced, heat load will be increased and in this case also oil temperature might be higher.

So, what we can say about the overheating of hydraulic system? Hydraulic system overheating is basically due to excessive heat load. 

If there is any pressure drop in the hydraulic system, we must understand that this loss in pressure will be converted in to heat energy and heat load will be increased and this is the basic reason behind overheating of hydraulic unit.

So what will be the desired solution for overheating of hydraulic system?

 

Solution of overheating issues in hydraulic system

As we know that, reason of a problem itself will have a solution and that’s correct, we have two processes for solving the overheating problem in hydraulic system.
  1.  Increase the heat dissipation capacity of system
  2.  Reduce the heat load
Out of above two processes, we recommend to reduce the heat load as if we are reducing heat load that means we are increasing the efficiency of system and reducing the inefficiencies of system.

We may also install an additional oil cooler for increasing the heat dissipation capacity of system. 

We must understand that overheating issues in hydraulic system is really very critical and it is quite possible the failure of various hydraulic components, if we run the hydraulic unit continuous under overheating situation.

Hence we must have to careful about the hydraulic system overheating problems and we must take shutdown for securing the root cause.

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