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Technical Paper

Comparison of Analytical and Experimental Investigations of a Hydraulic Multi-Circuit Sequential Apportioning System

1990-09-01
901553
In conventional hydraulic systems, a fixed or variable displacement pump is used to supply a number of separate branches of a circuit, each with potentially different flow rate and pressure requirements which can vary widely with time. Conventional approaches to distributing the flow to the individual branches generally involve valves controlling the flow to each individual branch. This can lead to significant energy losses from valve throttling, depending upon the actual flow and pressure requirements of each part of the circuit. In the system discussed in this paper, the entire output of the pump is quickly and sequentially directed to each individual branch of the circuit. The average speed of the actuator is controlled by the proportion of time that the pump flow is being directed to that branch. A small accumulator is incorporated in each branch of the circuit to smooth the velocity of the actuator.
Technical Paper

Positive Displacement Calibration for Laboratory Flowmeters

1995-09-01
952093
Positive displacement flowmeters can be used to simply and accurately calibrate common flow transducers such as axial turbine and target flowmeters. Two means of utilizing positive displacement devices were studied for use as a laboratory flowmeter calibration. The first method employed a fixed displacement axial piston motor. This proved unsatisfactory due to the difficulty in quantifying flow losses. The second method used a large hydraulic cylinder. An optical encoder measured the position of the cylinder rod, permitting a direct calculation of the flow through the in-line flowmeter being calibrated. Because cylinder leakage is virtually zero at low pressure, flow can be readily calculated knowing the effective cylinder diameter and piston velocity. The method described in this paper permits flow rates to be measured with an accuracy of ±0.1% of the volumetric flow rate. This paper discusses details of the design of the flowmeter and calibration method.
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