单项选择题
A.allow an alternate main pump to start in the fully loaded condition thus developing immediate full torque
B.prevent either main pump from being hydraulically motored when idle by cross pressure flow
C.prevent both units from operating simultaneously which could result in doubling the flow of oil and pressure leading to over pressurization of the system
D.all of the above
单项选择题 Although lube oils used in the main lubricating service systems should have a relatively high flash point to avoid ignition, they can create smoke and fire hazards when they（）
单项选择题 Compensated flow control or constant flow valves are used in hydraulic systems to（）
单项选择题 To avoid damaging the components of a printed circuit board when testing it with a DC volt-ohmmeter, you should （）