The Dynamic Performance of a Pilot Stage in the Poppet Type Hydraulic Flow Amplifier

• This paper examines the dynamic properties of the pilot stage in a poppet type two-stage flow control valve of the -Valvistor- type. The particular valve studied is a screw-in Valvistor valve of NG16 size. There are several benefits to this valve type: it has a high closed loop bandwidth and the design allows big flow capacities. An attractive feature of this two-stage valve is that the pilot flow contributes to the total flow giving higher steady state flow efficiency. The dynamic characteristics of the main stage were discussed in an earlier paper. In this paper the aim is to study the influence of the pilot stage of the valve. The bandwidth of this type of valve is often unexpected low. Due to the high bandwidth of the Valvistor element the pilot dynamics is often dominating. In this paper it is shown by measurements the influence of different parts in the pilot valve that limits its bandwidth. Flow forces are used in this valve to compensate the pressure dependency in the flow. It is a common way of design in so called pressure compensated valves. It is discussed in the paper how this flow forces influences the dynamic properties of the pilot valve. The mentioned flow forces interact together with the mechanical spring in the pilot valve. Although the studied valve is just one of many variants of the Valvistor principle, we will investigate it closely due to the interest for this valve among other researchers. One important conclusion is that the inductance of the pilot solenoid is often limiting the bandwidth of the valve as a whole. 

Nyckelord

valvistor

poppet valve

dynamic model

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