How to use the pressure drop method to detect the leakage in the Telescopic Hydraulic Hoist Cylinder
For the internal leakage inspection items of the telescopic hydraulic hoist cylinder during the factory test, the national standard GB/T15622-2005 "Hydraulic Cylinder Test Method"
In practice, the test method has problems such as repeated disassembly and assembly of oil pipes, inconvenient collection of internal leakage oil, and low test efficiency.
Telescopic Hydraulic Hoist Cylinder manufacturers have begun to use the pressure drop method to indirectly detect internal leakage instead of detecting the actual leakage. This method is simple and quick to operate and has strong operability.The key is high test efficiency, suitable for assembly line operation, especially for large-scale cylinder manufacturing enterprises
1 . The principle of pressure drop method to measure internal leakage
After the hydraulic pump (or booster cylinder) pressurizes the tested cylinder to the required test pressure, the electrical control system unloads the pressurizing system, and the hydraulic lock connected to the cylinder oil pipeline maintains the pressure of the tested cylinder. In the process, collect (or read, observe) the actual value of the pressure drop of the pressure gauge that measures the cylinder pressure during the pressure holding time,compare the qualified allowable pressure drop standard value of the oil cylinder to indirectly judge whether the leakage of the telescopic cylinder is qualified. This method is not to measure the actual internal leakage of the cylinder, but to indirectly judge whether the internal leakage of the cylinder is qualified through the comparison between the actual pressure drop value and the standard value.
2. Several issues that need to be clarified when measuring internal leakage by pressure drop method
When the pressure holding testing , the pressure is to be reduced, and the value of the pressure drop is collected (or read or observed). Sometimes I encounter some relevant personnel of users who think that the pressure in the oil cylinder should always be kept constant during pressure maintenance and cannot be reduced, otherwise, the telescopic hydraulic hoist cylinder will leak and fail.In fact, when maintaining pressure, there is a gap between the cylinder piston seal and the cylinder wall. If there is a gap under pressure, there will be leakage, and there will be a pressure drop.It's just that under the conditions of different cylinder sealing forms, different hydraulic valve forms, and different test pressures, the leakage amount is different, and the pressure drop is different.
3. How to formulate judgment standards
After determining the cylinder diameter, test pressure, pressure holding time, oil temperature, pressurization chamber and other test conditions, first check the internal leakage of the cylinder according to the national standard test method, and find the cylinder whose internal leakage meets the national standard (or enterprise standard) , In accordance with the pressure drop method to measure the pressure drop value of this qualified cylinder under the same test conditions, this value can be used as the standard value of the same type of cylinder under the same test conditions in the future enterprise. If the actual pressure drop value is higher than this value, it can be judged. If the leakage in the test cylinder exceeds the standard, the cylinder is unqualified; if the measured pressure drop is lower than this value, it can be judged that the leakage in the tested cylinder does not exceed the standard and the cylinder is qualified.
4. Revision of judgment standards
In summary, when the accuracy of the test results is high, the pressure drop standard must be more compatible with the test conditions. However, the correspondence between the standard value and the test conditions does not need to be too high. For example, when other conditions are the same, theoretically speaking, when the oil temperature changes, it will affect the test results. It is impossible to change once, so a standard should be developed. It loses the high efficiency and convenience of the pressure drop method, and the pressure drop is too small to be seen after a change of time; however, when the test conditions change greatly, the standard value must be revised. Our experience is that when the temperature is 10℃, the test pressure is 5MPa, the cylinder diameter is 50mm, and the pressure holding time is within 3 minutes, the same standard can meet the accuracy requirements of most companies. The extent to which the specific pressure test conditions change requires modification of the standard value is determined according to each enterprise's own situation.