2 - TCA spa

SEQUENCE VALVESFigure 6. Clamp CircuitCutterSequence ValvesClampOperationWhen operated fluid will flow to theclamp cylinder closing it. At the end ofits stroke, pressure will start to riseopening the sequence valve allowingflow to the knife. When the directionalvalve is switched to reverse theoperation flow will pass first to the knifecylinder and only when it has reachedthe end of its stroke will the pressurerise sufficiently to open the sequencevalve on the clamp line, allowing it toopen. Return flow in both operations bypassesthe sequence valve via the builtin check elements.Controlling the pressure in, or the flow from the drain lineopens up a number of possibilities. When using a pilotoperated version of the valve, closing the drain line will closethe valve. In this way, high flows can be turned on and off byusing a small solenoid valve situated on the drain line. This canbe a normally open or closed valve with the added option of acontrollable pressure drop across the valve.By controlling the pressure in the drain line, you can use thevalve in regenerative circuits, as below.When extending the cylinders, oil from the 'rod' side isprevented from passing back to tank by a check valve and isdirected towards the 'bore side' of the cylinder. The flow willthen pass through the sequence valve from the outlet to inlet.The pressure in the outlet will be higher than the inlet, which ishigher than the set pressure of the sequence valve. The drainline is connected upstream of the check valve so that whenretracting the cylinder, the working pressure increases thesetting of the sequence valve and keeps it closed.The main advantage of using the sequence valve over a pilotto close check, is that when centring the directional valve, thepressure can be set higher than any residual pressure, therebypreventing any un-solicited extension of the cylinder.This kind of valve can also be used as a compensator in apressure compensated flow regulator circuit (figure 8), wherebythe drain line of the sequence valve is connected downstreamof an adjustable orifice and the inlet of the sequence valveupstream, with the “sequenced” port connected to tank. Thepressure drop across the orifice is sensed by the spool in thesequence valve. The pressure on the upstream side acts onthe spool’s nose and pressure on the downstream side acts onFigure 7. Regenerative circuit