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Views: 0 Author: Site Editor Publish Time: 2026-08-07 Origin: Site
Flow rate is the central operating variable for a flow-operated hose burst valve. The valve is designed to remain open while hydraulic flow stays within the normal operating range and to close when flow rises above a calibrated threshold. That makes the relationship between normal flow, peak flow and actuation flow more important than simply choosing a valve with the correct thread size.
When hose burst valves are matched correctly, they add emergency load protection with little interference during ordinary machine movement. When the flow relationship is wrong, the valve may trip during normal operation, create unnecessary pressure loss, or react too late during a hose rupture. Understanding the different flow values in the circuit is therefore the foundation of correct sizing.
Many selection errors begin with a single number from the pump data sheet. If a pump is rated at 40 L/min, an engineer may assume the hose burst valve only needs to handle 40 L/min. That can be wrong because the flow through the protected actuator port can differ from pump delivery.
Cylinder area ratio, load-induced motion, regenerative circuits, accumulator discharge, pump displacement control and simultaneous functions can all change local flow. The valve must be selected for the actual flow passing through its installation point under the worst approved operating condition.
The actuation flow is the value at which the internal closing element becomes unstable in the open position and moves toward the seat. If the maximum legitimate operating flow is too close to this value, normal transients can cause nuisance closure.
A practical design therefore establishes a margin. For the Fuke LRV product, the technical recommendation is to set the closing flow approximately 50% above the maximum system flow. Other valve designs may use different margins, so the manufacturer’s data should always be followed. The important principle is that maximum normal flow and emergency closing flow must not be treated as the same number.
A machine cycle can have an average flow of 30 L/min while producing short peaks of 45 L/min. If a burst valve is set at 40 L/min, a conventional flow meter may show an apparently safe average even though the valve repeatedly sees a higher instantaneous value. Selection should therefore consider transient peaks, especially during rapid lowering, abrupt spool movement and load acceleration.
For a double-acting cylinder, the cap-end area is larger than the annular rod-end area. At the same piston speed, the cap side displaces more oil than the rod side. This simple geometry means that the outlet flow can be different depending on direction.
Suppose a hose burst valve is installed at the cap end of a load-supporting cylinder. During lowering, the piston may force a large volume of oil through that port. If the selection was based on rod-side flow or pump flow, the actual discharge can exceed the expected value. The valve then appears “too sensitive” even though the root problem is an incorrect flow calculation.
In an overrunning-load condition, gravity drives the actuator. The load can attempt to move faster than the pump is filling the opposite chamber, particularly if the control circuit does not adequately meter the motion. This can create a high outlet flow at the hose burst valve.
That behavior is why hose burst valves are not substitutes for every type of motion-control valve. The burst valve should remain open during approved lowering speed, while the broader hydraulic circuit should prevent uncontrolled acceleration during normal operation. If normal load-induced flow is unstable, raising the burst-valve setting alone does not solve the underlying control problem.
Flow rate through a restricted passage creates velocity. For a given flow, a smaller internal area produces higher velocity and generally higher pressure loss. An undersized hose burst valve can therefore create excessive pressure drop and operate closer to its closing condition even when the thread connection looks correct.
A larger valve may reduce pressure loss, but oversized selection also requires care. The selected actuation range must still be low enough for a real hose rupture to generate the required closing condition. Hydraulic sizing is a balance between passing normal flow efficiently and preserving reliable emergency sensitivity.
The pressure drop through an open valve increases as flow increases. Excessive pressure drop wastes hydraulic power and can generate heat. It also changes the pressure available to other parts of the circuit. A valve that operates with little restriction at 20 L/min may behave very differently at 70 L/min.
Manufacturers often provide pressure-drop curves at specified oil viscosity and temperature. These curves are more useful than thread size alone because they show how the valve behaves across a range of flows. When evaluating a machine with high duty cycle, the normal operating point should remain in a reasonable part of the flow curve rather than near the edge of the valve’s capacity.
Flow of 40 L/min does not create exactly the same hydraulic conditions with cold high-viscosity oil as with warm low-viscosity oil. Viscosity affects pressure loss, Reynolds number, internal damping and the force distribution around the moving element. A valve that is stable at operating temperature may be more prone to nuisance closing during cold startup.
Selection should therefore consider the full expected fluid-temperature range. If the machine operates outdoors, winter viscosity can be especially important. Correct oil grade, warm-up practice and adequate valve size help maintain predictable performance.
Directional control valves do not always open gradually. A fast spool, solenoid valve or aggressive joystick command can connect a loaded cylinder to return very quickly. The resulting transient may last only a fraction of a second but still exceed the hose burst valve’s closing threshold.
This is why commissioning should include realistic operator inputs rather than only slow laboratory-style movement. Test the machine across approved loads, engine speeds and control commands. If a valve trips only during the sharpest transition, the transient peak should be quantified before the actuation setting is changed.
A complete hose separation can drastically reduce downstream resistance. Pressure stored by the suspended load then drives oil out of the cylinder through the open failure. The flow rise depends on load pressure, hose size, rupture location, fluid properties and restrictions between the actuator and break.
A partial rupture may create a smaller increase than a fully severed hose. This is important because the actuation threshold must still support the machine’s defined safety objective under credible failure scenarios. Excessively high calibration can reduce nuisance trips but may also require a more severe leak before the valve closes.
A 3/8-inch or 1/2-inch thread identifies mechanical connection geometry, not one universal hydraulic flow. Different manufacturers can design substantially different internal passages behind the same port size. The same valve body may also be offered with different calibrated closing-flow ranges.
Use thread size to confirm mechanical compatibility only after hydraulic capacity and actuation range have been established. This avoids the common mistake of assuming that a valve matching the hose fitting automatically matches the flow.
Start with the fastest permitted cylinder speed under the most demanding approved load. Determine the displaced oil volume at the valve location and account for cylinder area ratio. Then consider pump speed, simultaneous functions and any transient increase caused by acceleration or control switching.
The resulting maximum normal flow becomes the reference for setting the valve. Apply the manufacturer’s recommended margin to establish the actuation target. If the required value falls outside the valve’s adjustable or calibrated range, select a different size rather than forcing the existing valve to an unsuitable extreme.
If measured maximum normal flow through the protected port is 60 L/min, the closing threshold must be clearly above that value. Using a product recommendation of approximately 50% margin would point toward an actuation value near 90 L/min, provided that the selected valve model supports that range and the machine’s hose-failure analysis confirms adequate emergency response. The example illustrates the method, not a universal setting for every circuit.
Whenever possible, measure flow close to the hose burst valve rather than assuming that pump output represents the same condition. Instrumentation should have enough range and response speed to capture transient peaks. Pairing flow measurement with pressure measurement can reveal downstream restrictions and load-induced behavior.
Testing should be carried out by qualified personnel with the load controlled and the machine in a safe condition. Creating an actual uncontrolled hose rupture is not an appropriate routine test method. Use manufacturer-approved functional tests or controlled simulation procedures.
A hose burst valve must distinguish between the highest flow the machine legitimately needs and the abnormal flow created by a dangerous line failure. Too little separation produces nuisance tripping; too much separation can reduce sensitivity. Correct sizing therefore depends on actual port flow, transient peaks, cylinder geometry, valve capacity, viscosity and pressure-drop behavior.
Ningbo Fuke Hydraulic Machinery Co., Ltd. manufactures hydraulic valve and fitting products for industrial and mobile systems. When specifying a hose burst valve, sharing the maximum normal flow, working pressure, oil viscosity, temperature range, cylinder configuration and connection details allows the actuation range to be matched to real machine conditions rather than to a nominal hose or pump size alone.
