Hydraulic filter bypass valve: what it does and what happens when it opens

Hydraulic systems form the basis of much industrial equipment, construction equipment, as well as agricultural vehicles and manufacturing processes. They depend upon clean fluids in order to perform efficiently and safeguard expensive components like motors, pumps, cylinders, valves, and pumps. A component that is often overlooked and plays a crucial role in maintaining the reliability of hydraulic systems is the bypass hydraulic filter valve.

Though it is small in terms of size, the bypass valve has an enormous impact on the performance of a system and the longevity of equipment. Knowing its function and how it functions and the process it takes to open and how it does can assist maintenance workers as well as operators and engineers avoid costly breakdowns and downtime.

What is a hydraulic filter? bypass valve?

A hydraulic bypass valve is a security device that detects pressure integrated into a filtering assembly or filter element. Its main purpose is to ensure that the hydraulic fluid is able to continue flowing through the system even after the filter's capacity is reduced.

When hydraulic fluid flows through a filtering system, pollutants such as dirt, metallic particles, dust, dirt, and wear debris are removed by the filtering media. In time, these particles are accumulated and add resistance to the fluid flowing across the filters. This resistance causes the pressure difference, often known as differential pressure, on the sides of the outlet and inlet that make up the filters.

Once the differential pressure has reached an appropriate level, the bypass valve opens automatically and allows for the hydraulic fluid to pass through and continue to flow throughout the entire system.

In the simplest words, the bypass valve functions as an emergency exit for hydraulic fluid in the event that the filter is too restrictive.

What is the reason a bypass valve is required?

At first the idea of allowing fluid that is not filtered to flow into the hydraulic system could appear to be counterproductive. However, the alternative may be far more damaging.

Hydraulic systems are dependent on the continuous flow of fluid. If a filter that is blocked blocks flow completely, then the following issues could result:

• Pump starvation

• Cavitation

• The loss of the lubrication

• Pressure in the system is decreased

• Shut down of equipment

• Severe component damage

The bypass valve has been created to eliminate these issues by prioritizing fluid flow over filtering in the event of a need.

Think of it as the mechanism that relieves pressure for the filter. It guarantees that hydraulic components continue to receive fluid, even when that fluid is temporarily not filtered.

What is a hydraulic filter? How does a bypass valve function?

The operation of bypass valves is fairly easy.

Normal conditions:

1. The hydraulic fluid is injected into the housing of the filter.

2. Fluid flows by the media filter.

3. Contaminants are sucked up by the filter.

4. Clean fluid is able to exit the filter and flows through the filter.

As contaminants build up, the filter becomes more impervious. As the pressure rises on the downstream part of the filter, it increases, but the pressure downstream remains lower.

The bypass valve has spring-loaded mechanisms that are calibrated to open when there is an exact differential pressure. Common settings for bypass valves vary from 15 to 50 psi (1.1 to 3.5 bar) dependent on the purpose for which it is being used.

If the pressure difference is greater than the valve's set-point:

1. The spring expands.

2. The valve is opened.

3. Fluid circulates around the filter element, instead of flowing through it.

4. The flow of hydraulic fluid continues unabated.

When the differential of pressure decreases to below the setting of the valve, the valve is shut and normal filtration begins.

The most common reasons why the bypass valve can open

The opening of a bypass valve doesn't always mean an issue, but it typically indicates that attention is needed.

1. Filter element clogged

The most typical reason is due to a component of the filter that is reaching its capacity to hold dirt.

As the accumulation of contaminants occurs within this filtering media, resistance grows up to the point that the bypass valve opens.

This can be an indication that the filter needs to be changed.

2. Cold hydraulic oil

Hydraulic fluid thickens when temperatures are low.

Colder temperatures make it harder for oil to flow through the filter media, causing an immediate drop in pressure over the filter. When the filter is first started in cold weather, the bypass valve could be opened briefly until the oil is warm and the viscosity drops.

This is normal in a variety of hydraulic systems.

3. Demand for flow is excessive

In the event that your system abruptly needs an increase in flow, it is possible that the filter won't be able to handle the amount of fluid without causing an excessive pressure differential.

In these instances the bypass valve could be opened temporarily to ensure adequate flow.

4. Filter selection is incorrect

Filters with an overly fine micron rating or a low flow capacity could result in an excessive restriction.

Even a filter that is clean can be a trigger for bypass when it isn't aligned in the system of hydraulics.

5. Hydraulic fluids contaminated with toxins

When the hydraulic oil is contaminated with an unusually high amount of contaminants, the load on filters accelerates quickly.

The filter will reach its capacity faster, increasing the probability of bypassing incidents.

How does the bypass valve work when it is opened?

When a bypass valve for a hydraulic filter valve is opened, a number of important events occur simultaneously.

Fluid continues to flow

The main purpose of a bypass valve is to make sure that the hydraulic fluid will continue to reach critical components of the system.

If this is not done, the flow might be slowed to levels that could be dangerous.

The amount of water that is filtered is decreased or eliminated

When the bypass valve opens, it will allow some or even all the hydraulic fluid to flow through the media, filtering it.

This means that contaminants that are normally retained can circulate throughout the system.

Concentrations of contaminants rise

Since the effectiveness of filtration is diminished as filtration effectiveness decreases, particle contamination levels begin to increase.

These substances can cause wear on delicate components.

The system's performance could remain normal

In many cases, operators notice no immediate change in machine performance.

The hydraulic system is functioning since the flow is maintained.

This can give an illusion of security, causing operators to miss the main maintenance issue.

Component wear increases

While short-term operations in bypass mode are acceptable, long-term operation could substantially add wear to:

• Hydraulic pumps

• Valves for servos

• Proportional valves

• Cylinders

• Motors

• Bearings

The cost of contamination over time usually exceeds the cost of replacing filters as scheduled.

Can it be safe to allow a hydraulic system to function with a bypass?

The answer is contingent on how long the system stays operating in bypass mode.

Short-term bypass operations are exactly what that valve was created to be used for. Short-term bypass operations in cold starts or short periods of high demand are usually acceptable.

However, the continuous operation of the bypass valve being open must be viewed as a warning sign.

The extended bypass operation may result in:

• Wear and tear on components has increased

• System efficiency is reduced

• Valve that is stuck

• Pump damage

• Reduced fluid life

• Unexpected failures

Maintenance staff should be able to identify any bypass issue that is recurring whenever possible.

How can you tell if the bypass valve is open?

Many hydraulic systems come with indicators that aid in identifying bypass operations.

Differential pressure indicators

These devices monitor the pressure drop across the filter and give either electronic or visual warnings when the filter is restricted.

Common indicators are:

• Mechanical gauges

• Pop-up indicators

• Electronic sensors

• Dashboard warning lights

Analysis of oil

Regular oil testing could reveal high levels of contamination, which suggest a prolonged bypass operation.

Particle count analysis can provide the early warning signs of problems with filtration.

Monitoring of performance

Unexpected increases in wear of components or recurring valve problems or decreased system reliability may be a sign of contamination due to bypass or other events.

How do you avoid the frequent bypass valve activation?

While occasional bypass operations are normal, the frequency of activation should be avoided.

Make sure to replace filters at the appropriate intervals.

Replace filters as per the manufacturer's recommendations instead of waiting for the onset of clogging to be severe.

Preventive maintenance is much more affordable than replacement of components.

Make sure to use the correct filter

Make sure to select filters that are in line with the specifications of the equipment manufacturer:

• Micron rating

• Capacity of Flow

• Pressure rating

• Bypass setting

Monitor the filter's condition

Inspect and replace the differential pressure indicators regularly.

These devices can provide valuable information on the health of filters before bypass operation becomes more frequent.

Maintain fluid cleanliness

The use of a contamination control method can significantly prolong the life of filters.

Recommendations for practices include:

• Proper fluid storage

• Proper filling practices for clean and safe use

• Sealed reservoirs

• Breather filtering

• Regular oil analysis

Make sure to warm up the equipment correctly

In colder environments, the process of allowing hydraulic oil to get to operating temperature prior to use may reduce unnecessary bypassing incidents.

The price of not addressing the bypass condition

Many hydraulic malfunctions can be traced to contamination.

Research studies in the field consistently indicate that the presence of particles is among the main reasons for failure of hydraulic components.

Inattention to a bypass issue could result in:

• Cost of replacing the pump

• Valve repairs

• More downtime

• More expensive maintenance costs

• The equipment's life expectancy is decreased.

A relatively low-cost replacement for a filter can save thousands in repair costs.

The bypass valve of the hydraulic filter is an essential component of protection that guarantees continuous flow of fluid in the event that filter restriction is excessive. When it opens at a certain threshold pressure differential, the valve helps prevent cavitation, pump starvation, and the possibility of system shutdowns.

But even though the bypass valve guards against the immediate failures of flow, it does this by allowing fluid that is not filtered to circulate throughout this system. The temporary bypass operation is usually acceptable, particularly in cold start-ups or short periods of peak demand. Regular or continuous bypass operations, however, should be considered an indication of maintenance.

Knowing why bypass valves open and observing the state of the filter regularly will help companies maintain more efficient hydraulic systems, prolong the life of equipment, and decrease the time between maintenance and expensive repairs. In the field of maintenance for hydraulics, bypass valves are not an emergency feature; it is vital to ensure balance between the flow of fluids and filtering in the event of operating conditions becoming difficult.