Hydraulic Valve Test Rig
The hydraulic valve test rig at ifas was built to enable valve measurements conforming to international standards. It accomodates test valves up to nominal size 20. All demands of ISO 4411 and parts of ISO 10770-1 have been realised. Furthermore, the possibility of measuring the position and the operation force of the spool is provided.
ISO 4411 of 1986 was developed by the technical committee ISO/TC 131 “Fluid Power Systems”. It defines how to determine the pressure difference due to a flow through an arbitrary path within the test valve under steady state conditions. The result is the functional relation between pressure difference and flow at a certain spool position. ISO 4411 establishes three classes of accuracy and defines the maximum error of each transducer. Class A has the highest demands, while class C has the lowest demands and is sufficient in most applications. These tests meet the requirements of class C.
ISO 10770-1Copyright: © ifas
ISO 10770 part 1 of 1998, was also developed by the technical committee ISO/TC 131 “Fluid Power Systems”. It replaces ISO 6404 of 1985 and describes methods of testing electrically actuated four-way directional valves. The main objective of ISO 4411 is the determination of characteristic values, respectively the relation between flow and pressure difference, which is important for the valve’s performance. In contrast, ISO 10770 focuses on different test methods to determine the marketability of valves. Nevertheless, it can be understood as a supplement to ISO 4411, because it provides concrete proposals for the hydraulic design of a test rig and, on the other hand, allows optaining additional valve properties.
The test rigCopyright: © ifas
The test rig is supplied with hydraulic energy by the institute’s biggest hydraulic power unit. The aggregate features 445 kW of installed electric power. By means of two variable displacement pumps and one constant displacement pump a maximum flow of 840 l/min can be generated. The maximum operating pressure is 350 bars. Due to the limited electric power and losses within the test rig, it is impossible to simultaneously reach both maximum flow and maximum pressure.
The figure below presents the test rig’s hydraulic diagram. All three pumps are merged into one symbol. The test valve is connected to ports “P”, “T”, “A” and “B”. The ports for the pressure transducers are placed five or ten times the nominal diameter D away from the test valve respectively. The connectors for the temperature sensors are positioned 15 x D times from the test valve. Thus, the distances meet the requirements of ISO 4411:1986.
The oil temperature (HLP 46) can be controlled by use of a separate cooling and heating circuit.The test rig offers the opportunity of testing each of the four metering edges separately or two in combination. If only one edge is tested, the oil is directed to the flow sensor after passing through the test valve. When testing two edges combinedly valve ports “A” and “B” are connected by the flow sensor (cf. ISO 10770:1998, p. 28).
By the use of a PI closed-loop control a control valve keeps the test valve’s pressure difference at a constant level. Thus, it is possible to determine e.g. flow rate as a function of a spool position or the input signal of a constant differential pressure level.