| 摘要 |
<p>An hydraulic unloading valve (V) for unloading hydraulic fluid from a circuit pressurised by a diesel engine powered pump (P) under cold climate conditions to assist starting of the engine (E). The valve has an inlet (13) through which fluid enters the valve, an outlet (14) through which fluid may leave the valve, an outlet valve seat (22), a valve member (15) movable towards and away from the valve seat and carrying a valve surface (23) for closing off the seat valve. A first orifice (18) is provided in the valve member which is sensitive to viscosity and which in response to the flow of fluid through the inlet generates a first pressure drop arranged to tend to move the valve member (15) away from the valve seat (22). A second orifice (20) is also provided in the valve member which is not sensitive to viscosity and which in response to flow through the inlet generates a second pressure drop arranged to tend to move the valve member (15) towards the valve seat to bring the valve seat and surface into contact to close-off flow through the valve outlet when the second pressure drop is greater than the first pressure drop. The pressure drop characteristics of the two orifices (18, 20) can be arranged so that at lower fluid temperatures (of say below -10 degrees C) the valve is held open up to higher fluid flow rates, thus relieving load on the engine and assisting cold starting.</p> |
