Bypass Hydraulics – the bypass valve for safety and maintenance

The bypass valve is a simple shut-off valve or adjustable throttle valve used in parallel with another hydraulic component. It is installed in a line that bypasses the hydraulic component. This achieves several objectives:

• Ensuring a minimum flow rate
• Protection against overpressure
• Maintenance capability without having to shut down the entire hydraulic system
  

Application

The bypass valve is used on hydraulic components that offer resistance to the flow of hydraulic oil. These can include:

• Filters
• Motors
• Other valves
• Complex piping with constrictions and bends

Bypasses can certainly be installed without a shut-off or throttle valve. However, the use of a bypass valve makes the bypass adjustable. The simplest type of bypass valve is the check valve. It opens in one direction at a specific pressure but reliably shuts off against backpressure.

Function in Practice

Hydraulic systems rely on continuous flow. Where pressure builds up, it is lacking elsewhere. The greater the pressure difference, the greater the risk of damage. This can remain unnoticed for a long time, such as damage caused by cavitation. In the worst case, the hydraulic system can simply burst at a certain point. Pressure differences, especially when they fluctuate significantly, can gradually destroy all types of seals.

Filters are typical components equipped with a bypass valve. Filters retain suspended solids from the hydraulic oil, causing the filter element to gradually clog. This also impairs the flow rate and increases the pressure upstream of the component. In the worst case, this leads to the filter shutting off completely. Without a bypass valve, this can lead to the destruction of the entire hydraulic system.

At that moment, the bypass valve allows the pressure to pass the filter but also bypasses the filtering function. It is therefore recommended to equip the bypass valve with an alarm function. If an open bypass valve and a clogged filter go unnoticed for too long, the suspended solids can cause significant damage inside the hydraulic system due to their abrasive effect.

Furthermore, the bypass valve allows the filter to be temporarily decoupled from the hydraulic system. Especially when changing filter cartridges, it is necessary to depressurize the line to the filter housing. With the bypass valve installed, normal operation of the hydraulic system can be maintained even during maintenance.

Hydraulic motors or control valves are also subject to wear, making maintenance or replacement necessary. At these positions, too, this can be made more convenient by using a bypass valve.

Bypass Hydraulics: The Challenge of Effective Application

However, implementing a bypass valve is not without effort. The costs for piping and components double at every point where this solution is applied. Furthermore, the volume of the hydraulic system increases. This must be compensated for with a corresponding amount of hydraulic oil and a correspondingly higher pumping capacity. Bypass valves therefore make hydraulic systems significantly more complex and expensive. For this reason, their use must be well-considered and precisely planned.