1. If the jaw is not correctly clamped, the sample shall be clamped symmetrically according to the requirements.

2. The quality of the jaw is poor and the teeth are damaged, which not only affects the different hearts of the jaw, but also makes the sample slip during the test, making the yield point difficult to identify. Replace the jaws at this time.

3. The lifting guide wheel is not adjusted correctly, so that the upper and lower jaws are not concentric. One inspection rod shall be processed. After the upper and lower jaws are tightened, measure with dial indicator based on two force columns until the adjustment is qualified. Change the oil with proper viscosity. Check whether the joints of the oil system are tightened. If the gasket needs to be replaced, it shall be replaced in time. If the oil pipe is broken, check whether the joint of the oil system is tightened. If it is necessary to replace the gasket, replace it in time. If the oil pipe is broken, the oil pipe with higher strength needs to be replaced. In addition, it is also necessary to observe whether the piston of oil delivery valve and overflow valve is jacked or installed reversely. Common faults: after the sample breaks, the pendulum falls back quickly, causing impact.