<p>A hydraulic fluid pressure operated control mechanism for controlling of hydraulic systems has a housing with a flow through cross-sectional area restricted by a drill hole in an open position of the control mechanism and a seat engageable by a throttle device for restricting the flow through cross-sectional area in a closed or throttling position of the control mechanism. The inwroughted seat for the throttle device is located in the conical bottom of a bore and has the form of a frustum of a pyramid having a plurality of sides.</p>
