Question

found on the outside of the jack. the major cause of external leaks is worn piston o - ring and/or worn piston. internal leaking means the hydraulic oil leaks inside the jack, from the pressure chamber to another low pressure area. this type of leak is evident by the self - dropping of the weight supported. this is often caused by a leaking release valve. identifying a leaking hydraulic jack. observe the outside of the jack for signs of relative fresh (moist) oil. the most common leak points are the piston o - ring, the release valve and the pumping valve. you can identity the severity of the leak by observing how much oil is on and underneath the jack. an excessive quantity and fresh oil on and underneath the jack where it is stored means there is severe leak and the jack should be removed from service. a small amount of old, dry accumulated oil near the piston however is considered normal, since the o - rings cannot completely prevent oil from going to the outside of the jack. to test for internal leakage, you can try to jack up some load with the jack in question. wait for 20 minutes, observing how much height the jack has lost. for a normal functioning jack, the height drop should be almost imperceptible. if the jack drops significantly and there is no obvious leaks on the outside then it is most like caused by a leaking release valve. important: the load youre jacking during this test should be stable; with a back - up support in place, to prevent the load from falling, should the jack suddenly fail. in what ways can the hydraulic system on a jack fail? external leaks. internal leaks. vapor lock.

Explanation:

The text mentions external leaks (worn piston O - ring and/or worn piston causing oil to leak outside) and internal leaks (oil leaking inside from high to low pressure area, often due to leaking release valve) as ways the hydraulic system on a jack can fail. There is no mention of vapor lock in the provided text.

Answer:

A. External leaks
B. Internal leaks