Pressure limiting valves

The pressure relief valve plays a crucial role in regulating the maximum pressure in hydraulic systems.

• Overload protection: Prevents the system pressure from exceeding a defined limit.
• Protection against damage: Reduces the risk of hose, seal and component failure.
• Safety component: Keeps the pressure within safe limits and increases operational safety.
• Extended system service life: Supports high reliability and extends the lifetime of the entire system.

Pressure relief valves open once the system pressure reaches the preset limit, thereby protecting the hydraulic circuit from overpressure.

• Pressure exceedance: When a defined limit pressure is reached, the valve opens.
• Diversion of flow: Excess fluid is discharged via a return line or directed back to the tank.
• Closing behaviour: When system pressure drops below the set value, the valve closes automatically.
• Spring-loaded closing mechanism: A spring holds the poppet against the pressure until the set value is reached.
• Bypass arrangement: The valve is usually installed in a bypass of the main circuit and acts as overpressure protection.

Using pressure relief valves offers numerous advantages in terms of safety, cost efficiency and system availability.

• Protection against costly damage: Prevents burst lines, seal failures and damage to pumps or actuators due to overpressure.
• Increased operational safety: Reduces the risk of malfunctions and increases process reliability.
• Personnel protection: Minimises hazards for operating personnel by limiting pressure spikes.
• Longer service life: Reduces stress on machines and components, thereby extending their useful life.
• Improved energy efficiency: Maintaining a constant pressure can reduce energy losses and increase overall efficiency.

Pressure relief valves are used in a wide range of mobile and stationary systems.

• Mobile machinery: e.g. construction machinery, municipal vehicles, industrial trucks.
• Industrial systems: Production and assembly systems, presses, machine tools.
• Agricultural machinery: Tractors, harvesting machines and implements.
• Pneumatics and other pressure systems: Protection of air and other media systems against overpressure.
• General hydraulic power units: In all systems where a defined maximum pressure must be maintained.

Pressure relief valves are designed for harsh operating conditions and therefore manufactured from robust, media-resistant materials.

Typical materials:

• High-strength steel for valve bodies and internal components.
• Brass or corrosion-resistant alloys for specific designs.
• Surface coatings (e.g. zinc plating, phosphating) to increase resistance to hydraulic fluids and corrosion.

Sizes and flow ranges:

• Compact valves for low flow rates up to approx. 60 l/min.
• Larger, pilot-operated valves for high flow rates and precise pressure control.
• Versions for different port sizes suitable for line-mounted or manifold/block installation.

For reliable pressure limitation, valves must be carefully matched to the respective application.

Selection criteria:

• Maximum working pressure: Must match the planned system pressure and required safety margin.
• Medium: Material selection must be suitable for the medium (e.g. hydraulic oil, water, air).
• Size and flow rate: Dimensioning according to the maximum expected flow.
• Adjustment range and fine-tuning: Fine adjustment of the opening pressure to meet system requirements.
• Standards and certifications: Compliance with relevant standards such as DIN, ISO or PED.
• Installation type: Line-mounted, subplate-mounted or screw-in valve, depending on the system architecture.

Pressure relief valves are generally low-maintenance but require regular inspection and maintenance intervals to ensure long-term reliability.

Scope of maintenance:

• Regular functional tests and checking of the opening pressure.
• Inspection for leakage and external damage.
• Inspection of springs, seals and seating surfaces during scheduled maintenance.

Service life:

• Depends on operating conditions, pressure loading and switching frequency.
• With proper use, clean medium and regular maintenance, valves often achieve a service life of many years up to several decades.

Below is an example data sheet for line-mounted pressure relief valves:

Example 1 – G 1/2" ports:

• Design: Line-mounted pressure relief valve.
• Port size: G 1/2".
• Max. flow rate: 70 l/min.
• Max. operating pressure: 300 bar.
• Setting range: 80 – 300 bar.

Example 2 – G 3/4" ports:

• Design: Line-mounted pressure relief valve.
• Port size: G 3/4".
• Max. flow rate: approx. 90 l/min.
• Max. operating pressure: 300 bar.
• Setting range: 80 – 300 bar.

The exact values may vary depending on series, manufacturer and design.