Safety valves (overload valves)
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Hydraulic safety valve, overload valve
What is a safety, relief, or overload valve?
Hydraulic relief valves, available in the Hydron offer, are components of hydraulic systems that provide protection against overloads by controlling the maximum pressure level in the system. Our valves, made of the highest quality materials, are a reliable solution for various industrial and hydraulic applications. A group of hydraulic overload valves whose task is to ensure constant limited oil pressure. Excess pressure is discharged into the relief line. The valves protect power hydraulics components from damage or destruction. Valves with a regulation function.
Operating principles of relief valves.
The relief valve regulating oil pressure in a hydraulic system is designed to maintain a constant pressure within it. The valves protect our hydraulic system against sudden pressure spikes. The valves have a regulation function (adjustment via a knob). They have an outlet allowing the installation of a pressure gauge to check the pressure. The valves feature a supply connected to the pump as well as an outlet and a relief port. The relief valve is mounted in the hydraulic system between the pressure line (port P) and the tank (port T). When the system pressure exceeds the set value, the valve opens, allowing the excess oil to flow into the tank. Thanks to this, the system pressure remains at a safe level.
Overload and safety valves – effective protection of hydraulic systems
The category of overload valves (also called safety, relief, or surge valves) in the HYDRON online store is a comprehensive selection of professional control components, created for the constant protection of power hydraulics systems against dangerous increases in operating pressure. Exceeding the maximum pressure in the installation can lead to costly and dangerous failures – rupture of pressure hoses, damage to actuator seals, damage to the pump body, or cracking of valve blocks. The task of the overload valve is to automatically open the flow and drain excess oil into the tank when a critical, pre-set value is reached.
Types of overload valves in the HYDRON offer
Depending on the construction of the hydraulic system and the expected functionality, you will find valves from renowned Italian and European manufacturers (e.g., Oleodinamica Marchesini, Luen) in our range:
Relief / overload valves (VMP / VMPP Series):
- Operating principle: Three-way safety valves connected directly to the pressure line. In the event of an overload, they open the relief port (T), directing excess fluid to the tank.
- Features: Equipped with a precise adjustment knob secured with a lock nut and a dedicated 1/4" BSP port for connecting a measuring manometer.
- Thread sizes: G 3/8", G 1/2", G 3/4", and G 1" BSP.
- Pressure regulation ranges: From 10–50 bar, 10–180 bar, 50–250 bar, 80–300 bar up to 50–400 bar (flows from 12 to 90 l/min).
Overload-blocking and brake valves (VBCD SE / DE / FLV Series):
Operating principle: Advanced valves combining an overload protection function with a hydraulic lock (blocking) and brake function. They ensure smooth and controlled load movement (preventing cavitation and uncontrolled actuator descent).
Variants:
- SE (Single Effect) – single, for single-acting receivers.
- DE (Double Effect) – double / twin, for double-acting receivers.
- FLV – versions with a hollow mounting bolt for direct screwing into the actuator body (e.g., in TUR loaders).
Also used as brakes and rotation locks for hydraulic motors.
Two-pump unloading valves (VABP Series):
Specialized valves used in systems powered by two pumps (low- and high-pressure). After reaching the set pressure, the valve automatically unloads the pump with the higher output, redirecting its flow to the tank.
Key advantages of HYDRON overload valves:
- Fast and repeatable reaction: Precisely ground, hardened internal elements guarantee instantaneous opening and closing of the flow at the set pressure.
- Simple and safe adjustment: Ability to accurately adjust the opening pressure using a screw/knob with a lock nut, which prevents self-adjustment due to vibrations.
- Durable galvanized steel: Bodies made of high-grade steel protected by a zinc coating, resistant to mineral oils, moisture, and harsh weather conditions.
- Wide temperature range: Trouble-free operation in oil temperatures from -20°C to +90°C (ambient from -40°C to +60°C).
Application in agricultural, construction machinery, and industry:
Safety valves from our offer are commonly used in:
- Front loaders (TUR), cyclops, and telescopic loaders (arm protection against excessive weight).
- Sweepers, snow plows, and sprayers (protection of steering and unfolding actuators).
- Hydraulic presses, wood splitters, and winches.
- Forklifts, excavators, and municipal vehicles.
- Stationary power units and industrial systems.
How to connect a VMP relief valve in a system?
- Ports P (pressure line): Connect the valve in parallel to the supply line of the circuit on which you want to control the maximum pressure (two P ports allow for flow-through connection into the manifold).
- Port T (relief / return): Connect directly to the pressure-free return line leading to the oil tank.
- Port M (optional): Screw in a 1/4" NPT/BSP glycerin manometer for constant monitoring of the set opening pressure.
Frequently Asked Questions (FAQ)
How is the pressure set on the VMP valve? The valve setting should be matched to the maximum operating pressure of the weakest element in the system (e.g., pump or hose). Turning the adjustment screw clockwise increases the opening pressure (e.g., in VMP 3/8" models, a full turn changes the setting by approx. 30–45 bar).
What is the difference between a VMP relief valve and a VBCD blocking valve? The VMP valve protects the system only against overpressure by releasing oil into the tank. The VBCD valve additionally functions as a lock (holds the actuator in a constant position when the directional valve is off) and controls the weight descent movement, preventing uncontrolled jerking.