If hydraulic fluid is the lifeblood of your system, hydraulic fluid contamination is its Achilles heel. That’s because even unseen, microscopic particulate matter in the fluid can bring colossal machines to their knees. In this war against contamination, the hydraulic filter is your first and only line of defence. When in good condition, filters will diligently remove debris and contaminants from the fluid - protecting your valuable machinery and saving you untold thousands in repair costs.

However, your filters are always fighting a losing battle. The more they operate, the more the contamination levels rise and eventually they become too fouled to perform correctly. When this happens, your filter is no longer able to protect the sensitive reciprocating parts in your system such as seals, piston surfaces, pump vanes, and other components. Leading to increased wear. 

Thus, replacing your hydraulic fluid filters regularly is an important practice, but it’s also important to optimise the frequency of replacement to maximise the value of your filters and to keep your maintenance costs low. Replace too early and your maintenance costs will increase unnecessarily. Replace too late and you run the risk of damaging your hydraulic machinery. So, how can one maintain a watchful eye over the contamination levels of your hydraulic filters? That’s the job of the clogged filter indicator.

The clogged filter indicator is a device which may be fitted to any hydraulic filter, which provides visual verification of the contamination levels within. It’s a small, clever component that could save you thousands in maintenance costs over the long term. That’s why it’s an important weapon in your fight against fluid contamination.

How clogged hydraulic filter indicators work:

Clogged filter indicators are also known as Differential Pressure Indicators - for a good reason. They measure the pressure on the inlet side of the filter element and compare it to the pressure on the outlet side. This difference between pressures gives an indication of how easily the fluid is able to pass through the filter element.

The more clogged the filter, the more it restricts the fluid flow. Thus, the fluid on the outlet side will become progressively lower in pressure as the contamination levels rise. When the pressure falls below a certain level, it triggers a signal that it is time to change the filter.

There is a wide range of clogged filter indicators available, but here are two of the most common examples.

Mechanical Pop-Up Button Type:  

Mechanical filter indicators utilise a magnetic system. A spring-loaded button is held down by a magnet attached to a piston within a tube. As the pressure lowers on the outlet side, it withdraws the piston. Consequentially, the magnet moves progressively further away from the button. As it does so, the magnetic force weakens. At a certain point, the distance becomes too great and the spring pressure exceeds the magnetic force and the button pops up. Providing a simple visual indication to the maintenance engineer that contamination levels have been exceeded. In this system, the button will remain extended even if pressure returns to normal - and must be manually reset.

Electrical Microswitch Type:

Electrical switches operate on the same principle with the magnet-piston arrangement, however, in this case, the magnet performs in such a way as to complete an electrical circuit, which sends a signal to a visual indicator. Depending on the model, this indicator could be as simple as a light. In other cases, it may connect to a computer system, which monitors the device remotely.

The advantage of electronic clogged hydraulic filter indicators is that they are more versatile and have the ability to reset automatically. Thus, they can accommodate for things like pressure differentials created during cold-start situations.

 In a cold-start situation, the fluid pressure differential may initially be too low, but will return to normal levels once the fluid reaches operating temperature. In this case, a Single Pole Double Throw Switch features a red and green light. When the pressure differential is within acceptable limits, the green light is illuminated. If the pressure differential is too low, the red light illuminates. In the cold start situation described above, the light would appear as red, but change back to green when pressure normalises as the fluid heats up. Thus, this type of electrical pressure differential switch can also perform the function of a system warm-up indicator.

Save your equipment & save on maintenance costs

As you can tell, the humble clogged filter indicator plays a significant role in the health of your equipment and the state of your maintenance costs. So it pays to select the right type for your application and your situation and to pay attention to what they’re telling you. Berendsen offers a wide range of these components from our principle supplier - Pall Corporation - among other brands. For information and advice on selecting the right indicator for your needs and your machinery, please contact our sales department who will be glad to assist you.