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What Are Hydraulic Pressure Relief Valves And How To Test
Modular hydraulic pressure relief valve and hydraulic cartridge pressure relief valve are available in almost all hydraulic systems, so it is of import to accept a total and deep agreement of the characteristics of the relief valve used.
Hydraulic Relief Valve Function and Application
Hydraulic relief valve consists of valve housing A, valve poppet B and spring C and other bones components, at least there are one inlet (P) port and one outlet (T) port. The main role of hydraulic pressure relief valve is substantially pressure limiting: to limited the working pressure is past pressure relief.
The load determines the pressure, the hydraulic relief valve only limits the pressure of the hydraulic system, simply the pressure level relief valve itself cannot generate pressure.
Basic Mutual Features Of Various Types Of Hydraulic Pressure Relief Valves:
one) When the inlet force per unit area reaches the force per unit area presetting point, the pressure level relief valve will open and relief the pressure then.
2) The bound bedchamber is by and large connected to the outlet port and the back pressure is equal to the outlet pressure. Therefore, in addition to the type of unloading exterior, the pressure level at outlet port is directly increased by one:1 proportion. If yous want the opening pressure level to exist completely contained of the outlet pressure level, y'all should consider using a sequence valve.
Basic Functions Of Hydraulic Relief Valves:
A. Equally a condom valve used to limit the maximum pressure of hydraulic system, information technology plays the following part:
1. Avert the high pressure amercement to the hydraulic system, components and piping
2. Avoid hydraulic power source such as electric motors, diesel engines, or gasoline engines stops while performance due to heavy loads
iii. Avoid excessive force/torque generated past the hydraulic cylinder or hydraulic motor, which may damage connected or pushed components; Avoid hydraulic cylinder or hydraulic motor with big inertia load, due to excessive inertial forcefulness during dispatch braking or torque, resulting in harm.
In these operating atmospheric condition, the pressure relief valve is commonly closed.
B. Equally pressure command valve, hydraulic pressurepressure relief valves maintain the pressure in whole hydraulic organization or partial system within a specific level or range, for case:
1. Relief flow for the inlet and outlet throttling speed control circuit, which can be referred to as the constant pressure valve at this time
two. Generate the back pressure on the return oil to improve motion stability, which is oftentimes referred to every bit back pressure level valve.
3. Unloading the force per unit area in double pump circuit or accumulator excursion, which is often referred to as pressure unloading valve.
In these conditions, the hydraulic pressure relief valve is unremarkably open.
There are many types of hydraulic pressure relief valves, which can be classified from many different angles.
Classification according to valve poppet construction:
1) Ball type: The ball blazon relief valve is simple in structure and low in cost, only information technology is only suitable for small menstruum.
2) Poppet type: The poppet hydraulic pressurerelief valve tin pass through a large flow, with less leakage, quick response and longer life, it is most widely used.
three) Spool type:The spool type relief valve can catamenia through a larger volume but with a smaller pressure range regulation.
Classification According To The Type Of Action
1) Direct acting pressure relief : The direct-interim type has fast response and pocket-sized overshoot and is suitable every bit a safety valve to reduce the impact, just the force per unit area regulation deviation is large, that is, the command pressure fluctuates profoundly with the period rate.
2) Pilot operated pressure relief:The pressure regulation deviation of pilot blazon is small, control pressure accurateness is high, and information technology is used in occasions where pressure control is more accurate needed, but the response is slower
3) Soft force per unit area relief blazon : Soft pressure relief blazon will be able to relief the pressure before the force per unit area reaches to presetting value and surges in the inlet port.
The force per unit area relief valve in the abiding rate pump with the open central spool directional control valve, or the (constant pressure) variable pump with the closed neutral directional control valve circuit more often than not requires a low leakage, fast response, anti-pollution, vibration reduction, can be considered using direct-acting type.
In the hydraulic constant rate pump throttle circuit, continuous catamenia supply and high-precision pressure level control are generally required. When small amounts of internal leakage accept piddling effect, pilot type pressure relief valves may be considered.
Classification According to the location of the application in the loop
1) Main hydraulic pressure relief valve, installed in the same direction of directional valve, the side of the hydraulic pump
2) Secondary hydraulic pressurerelief valve mounted later the directional valve, the side of driving device
Nomenclature co-ordinate to function
one) Normal type
ii) Pressure-rubber type. After opening, information technology volition not be closed until the inlet pressure drops to nothing. Not suitable for circuits that crave load property.
3) With opposite check valve type. The general relief valve does not pass in the contrary direction.
4) Bi-directional type. In the hydraulic motor drive excursion, the force per unit area relief valve, or a two-manner relief valve, should generally be installed on both sides to preclude excessive pressure on one side due to external loads during neutral conditions.
5) External control type. The opening pressure tin can be inverse by an additional control type such as a hydraulic control, air control, a solenoid switch, or an electric proportional command.
* There is as well a so-called thermal protection relief valve. Actually, it is a small straight flow relief valve that is used as a safety valve. It starts to relief the pressure level when the temperature rises causing thermal expansion of the closed liquid to protect the components (mainly hydraulic cylinders) from high pressure level damage.
From the point of oil connectedness, ordinary types are two-way. The 3-port and four-port ports are generally available for external control.
Differential Pressure Menses Characteristics Test For hydraulic pressureRelief Valve
(ane) Test circuit
See the effigy according to 1S003:1988 and GB/105-1987
one. Hydraulic ability source. Information technology is required that the flow rate be smoothly adaptable throughout the examination range, which is difficult to achieve with a single variable pump or a stock-still pump with a speed control valve. Particularly in the initial phase, because the required flow rate is very small, information technology is oftentimes beneath 0,i Fifty/min. Using multiple speed command valves in parallel, or featherbed throttle valve can accept in to consideration.
ii. The pressure relief valve in the organization is used for safety protection simply. The pressure set value must be higher than the exam range, only information technology does not exceed the allowable pressure level of the valve under examination.
4.Thermometer
5. Pressure sensor. 5a measures the inlet pressure level. 5b measures the outlet force per unit area. If the outlet pipe is very short, thick, the pressure loss is negligibly small fifty-fifty tin can be omitted. Or merely by a low pressure gauge is used for monitoring.
6. Tested valve
7. Flow sensor. Gear flow sensors may exist considered here because they accept a much larger measurement range than turbine flow sensors.
8. 10-Y recorder, or digital oscilloscope, or computer data acquisition tape display system.
Test Process Of Differential Pressure level Flow Characteristics
Preparation phase:
Connect the X-Y recorder with flow qv7 as the X axis, differential pressure P5a-P5b or pressure level P5a as the Y axis. Allow the oil temperature to reach the predetermined value.
Test procedure:
1. Plow on the hydraulic pressure source
ii. The tested valve 6 is adjusted to the minimum value of the given pressure adjustment range.
3 start recording. Slowly increase the output flow of the hydraulic source from zero to the maximum test flow, then slowly decrease information technology to aught and stop recording. 4. The tested valve 6 is adjusted to the maximum value of the given pressure level adjustment range and the steps are repeated step three.
five. Set a few more than values betwixt the maximum and minimum values of the pressure aligning range and repeat step 3.
*Continue the oil temperature relatively abiding throughout the test. The test curve thus obtained is the valve'due south characteristics under the operating conditions of the valve, which is typical test curve.
Transient Response Characteristics Test Of hydraulic pressurePressure Relief Valves
Test circuit: According to ISO03:1988 and GB/T8m5-1987:
- Hydraulic power source. It is best not to use a variable pump to avoid the dynamic response characteristics of the variable mechanism affecting the test results.
- The system pressure level relief valve is for condom protection only. The pressure level presetting value must be significantly higher than the exam range. Pressure relief should non occur during the test, otherwise information technology will reduce the arrangement pressure ascent gradient.
- Featherbed valve. Where 3a is used for pressure loading, it must be a quick-response valve, otherwise it will non be able to obtain a sufficient slope of system force per unit area rise. 3b is used to control the pressure in the airplane pilot chamber of an externally controlled relief valve. This part of the circuit must be modified accordingly with the blazon of valve existence used.
- Thermometer.
- Pressure sensor. Response characteristics meliorate than 5000Hz
- The valve being tested.
- Catamenia meter. If the menstruum is known, it can be removed or moved to the return line of the tested valve in order to reduce the volume of the pipe.
- Throttle valve. Set up initial force per unit area.
- Aught flow display. Information technology is used to monitor whether the menses bypasses the examination. Information technology can be a measuring cup or an ordinary container.
- Quick recorder. If digital, sampling fourth dimension is shorter than 0.2ms.
Testing Process:
Preparation:
one. Connect the pressure level sensor output P5 to the quick recorder.
ii. Start the hydraulic power source. Allow the oil temperature to reach the predetermined value.
3. The tested valve 6 under is adjusted to a certain opening pressure.
4. Bypass valve 3a open. Using the throttle valve 8 to set the initial pressure, information technology should approach but not exceed the opening pressure of the valve half dozen nether test.
Test Procedure:
one. At the beginning of the test, the flow from the hydraulic power source 1, is directly drawn through the featherbed valve 3a and the inlet pressure P5 of the valve under test is lower than the opening pressure and is closed by the tested valve 6 .
ii. Speedily close the bypass valve 3a, P5 quickly rises, open the tested valve 6. Afterwards a while, P5 has stabilized. By recording the transient changes in pressure P5, the transient behavior of the tested valve will be able to be seen.
3. If the pressure in the pilot chamber of the tested valve is externally controlled, the bypass valve 3b can exist rapidly connected to make the measured half dozen unloaded. P5 quickly decreased, which tin can measure the transient characteristics of the tested valve when unloading the pressure
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Source: https://www.finotek.com/hydraulic-pressure-relief-valves-and-testing/
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