Pilot operated poppet valves are a type of hydraulic valves that use a small pilot valve to control the opening and closing of a larger main valve. They are also known as pilot-to-open or pilot-to-close valves, depending on the direction of flow when the valve is de-energized.
How do pilot operated poppet valves work?
Pilot operated poppet valves consist of two main components: a main poppet and a pilot stage. The main poppet is a spring-loaded, pressure-balanced disc that seals against a seat to block or allow the flow of fluid between two ports. The pilot stage is a solenoid-operated valve that controls the pressure in a control chamber on one side of the main poppet.
When the pilot stage is de-energized, the control chamber is connected to the low-pressure port, and the main poppet is held closed by the spring force and the pressure difference across the poppet. When the pilot stage is energized, the control chamber is isolated from the low-pressure port, and the pressure in the control chamber drops due to a small orifice. This creates a pressure imbalance across the main poppet, which overcomes the spring force and opens the valve.
The opposite operation occurs for pilot-to-close valves, where the pilot stage is normally open and the main poppet is normally open. When the pilot stage is energized, the control chamber is connected to the high-pressure port, and the main poppet is forced to close by the pressure difference and the spring force.
The following table summarizes the operation of pilot operated poppet valves:
| Pilot Stage | Control Chamber | Main Poppet | Flow Direction |
|---|---|---|---|
| De-energized | Low-pressure port | Closed | No flow |
| Energized | Isolated | Open | Port 1 to Port 2 |
| De-energized | High-pressure port | Open | Port 2 to Port 1 |
| Energized | Isolated | Closed | No flow |
What are the advantages of pilot operated poppet valves?
Pilot operated poppet valves have several advantages over other types of hydraulic valves, such as:
- They have low leakage due to the tight seal between the poppet and the seat. This makes them suitable for load holding applications, where minimal fluid loss is desired.
- They have low pressure override, which means that the valve can open or close at a low pressure difference between the ports. This reduces the power consumption and the heat generation of the hydraulic system.
- They are adjustable under pressure, which means that the opening or closing pressure of the valve can be changed by adjusting the spring force or the pilot pressure. This allows for fine tuning of the valve performance and the system response.
- They have fast response, which means that the valve can open or close quickly in response to the pilot signal. This improves the dynamic behavior and the accuracy of the hydraulic system.
- They are dirt tolerant, which means that they can handle some degree of contamination in the fluid without affecting the valve function. This reduces the maintenance and the downtime of the hydraulic system.
What are the applications of pilot operated poppet valves?
Pilot operated poppet valves are widely used in various hydraulic systems, such as:
- Pressure relief valves, which limit the maximum pressure in a hydraulic circuit by opening when the pressure exceeds a set value. Pilot operated poppet relief valves have low leakage, low pressure override, and fast response, which make them ideal for protecting the hydraulic components from overpressure.
- Ventable relief valves, which are similar to pressure relief valves, but have a third port that allows the venting of the control chamber to the atmosphere or to another pressure source. This enables the remote control of the relief pressure by changing the pilot pressure. Ventable relief valves are useful for applications that require variable pressure settings, such as load sensing systems or pressure compensated pumps.
- Sequence valves, which control the sequential operation of two or more hydraulic actuators by opening when the pressure in the upstream circuit reaches a set value. Pilot operated poppet sequence valves have low leakage, low pressure override, and adjustable under pressure, which make them suitable for ensuring the correct order and timing of the actuator movements.