The top symbol shows a direct operated (single stage) directional valve with all ports blocked in the centre position. When the electrical solenoids are operated the spool position moves to either the right or left-hand position, allowing the different symbol logic to be employed. Note how the valves all have two springs so that with no signal to the valve, it will sit in its central, standby position. They are all shown at standby in their centre positions. Not all valves will operate or work safely without a low-pressure drain signal.Īll symbols show four-way three position valves. When using valves that switch pressure lines, without a direct, low pressure, return line connection it is important to make sure that the valves solenoid and spring chambers are rated for the maximum pressure they may see. The bottom symbol shows a hydraulically operated valve, but in this case, flow can only pass in one direction because the spring chamber is connected to the low pressure, return line connection. The middle symbol shows an electrically operated valve which is 'Normally Open' (NO). When activated the left-hand box would be connected to the pipes and flow could pass through the valve. in its standby condition, the right-hand box is connected to the pipes and no flow can pass through (closed). This top valve, therefore, shows a 'Normally Closed' (NC) valve e.g. pushed over by the spring, not the solenoid. Valves should always be drawn in the de-activated position e.g. The double arrow in the left box shows that the flow may pass in both directions.

The top symbol shows a manually activated valve that is pushed over against a spring. This means they have two flow pipe connections and can switch into two different positions. The valves shown are all two way, two position directional valves.

Hydraulic symbols chart download