초록

An apparatus for controlling flow of a fluid having two speed-controlled positive displacement devices for supplying a load with fluid under pressure from a supply at a different pressure with interposed variable-volume buffer containers.

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1. Apparatus for controlling the flow of a fluid from a fluid supply at a supply pressure, including a first positive displacement device connected to the fluid supply to deliver fluid to a load at a specific load pressure different from the supply pressure, a second positive displacement device arr

1. Apparatus for controlling the flow of a fluid from a fluid supply at a supply pressure, including a first positive displacement device connected to the fluid supply to deliver fluid to a load at a specific load pressure different from the supply pressure, a second positive displacement device arranged to receive fluid from the load and to deliver the fluid at the supply pressure, and means to control the speed of the positive displacement devices to control at least one of the parameters of the fluid in the load including the flow of fluid therein and the load pressure, wherein the improvements comprise a first buffer container capable of containing a variable volume of said fluid connected to the delivery of the first positive displacement device, and a second buffer container capable of containing a variable volume of said fluid connected to the input of the second positive displacement device to receive fluid from the load, and wherein the control means constrain the movable members of the positive displacement devices to operate, in use, at a single, constant speed and means are provided which control the passage of fluid through the apparatus, in use, by alternation between keeping the movable members stationary and allowing them to operate at said constant speed. 2. Apparatus for controlling the flow of a fluid from a fluid supply at a supply pressure, including a first positive displacement device connected to the fluid supply to deliver fluid to a load at a specific load pressure different from the supply pressure, a second positive displacement device arranged to receive fluid from the load and to deliver the fluid at the supply pressure, and means to control the speed of the positive displacement devices to control at least one of the parameters of the fluid in the load including the flow of fluid therein and the load pressure, wherein the improvements comprise a first buffer container capable of containing a variable volume of said fluid connected to the delivery of the first positive displacement device, and a second buffer container capable of containing a variable volume of said fluid connected to the input of the second positive displacement device and switching means arranged to cause at least said one of the positive displacement devices to cease discharging fluid to the first buffer container when a predetermined greater volume of fluid is in the container, but to re-start discharging fluid into the said container when a predetermined lesser volume of fluid is in the container, said switching means being arranged to cause the said one of the positive displacement devices to cease discharging fluid and being arranged, after a delay, to cause valves to close to prevent fluid from entering or leaving the apparatus. 3. Apparatus for controlling the flow of a fluid from a fluid supply at a supply pressure, including a first positive displacement device connected to the fluid supply to deliver fluid to a load at a specific load pressure different from the supply pressure, a second positive displacement device arranged to receive fluid from the load and to deliver the fluid at the supply pressure, and means to control the speed of the positive displacement devices to control at least one of the parameters of the fluid in the load including the flow of fluid therein and the load pressure, wherein the improvements comprise a first buffer container capable of containing a variable volume of said fluid connected to the delivery of the first positive displacement device, and a second buffer container capable of containing a variable volume of said fluid connected to the input of the second positive displacement device to receive fluid from the load and wherein both said buffer containers are airtight and joined by an air duct through which air moves between them to take up the volumes in them not occupied by the fluid. 4. Apparatus for controlling the flow of a fluid from a fluid supply at a supply pressure, including a first positive displacement device connected to the fluid supply to deliver fluid to a load at a specific load pressure different from the supply pressure, a second positive displacement device arranged to receive fluid from the load and to deliver the fluid at the supply pressure, and means to control the speed of the positive displacement devices to control at least one of the parameters of the fluid in the load including the flow of the fluid therein and the load pressure, wherein the improvements comprise a first buffer container capable of containing a variable volume of said fluid connected to the delivery of the first positive displacement device, and a second buffer container capable of containing a variable volume of said fluid connected to the input of the second positive displacement device to receive fluid from the load, and wherein at least one said buffer container includes a diaphragm and a constant force spring acting on said diaphragm to pressurize said container, both said buffer containers being arranged adjacent one another and including a movable barrier between said containers such that as one container increases in volume the other container decreases in volume and vice versa.