PREFILL VALVES
Fossa prefill valves are mounted on large hydraulic presses to fill the main cylinder quickly during the fast approach stroke.
On large presses the main cylinder holds a very large volume of oil: filling it with the pumps alone would require huge flow rates and long cycle times. The prefill valve solves this by connecting the cylinder directly to the tank above it.
During the fast approach the valve is open and oil flows from the tank into the cylinder at high flow and low pressure. When the slide reaches the workpiece the valve closes and the pumps pressurize the cylinder for the pressing stroke. On the return stroke the pilot piston opens the valve and the oil flows back to the tank.
Prefill valves
Fast filling of the main cylinder, tight sealing during pressing, decompression and return
HOW IT WORKS
- Fast approach: the slide descends by gravity or is pushed by auxiliary cylinders; the vacuum in the main cylinder opens the valve and oil flows in from the tank.
- Pressing: the valve closes and seals while the main cylinder works at operating pressure.
- Decompression and return: the pilot piston opens the valve in a controlled way, releases the pressure and lets the oil flow back to the tank as the slide rises.
CONSTRUCTION FEATURES
Steel valve body, tank connection flange, large-section poppet and integrated pilot actuator.
Each valve is custom designed for the cylinder volume, the cycle times and the space available on the press, with ports and flanges agreed with the customer. As for our cylinders, design, machining, assembly and testing are all carried out in-house at Silvio Fossa S.p.A.
ADVANTAGES
- Shorter cycle times thanks to fast filling of the main cylinder
- Pumps and circuit sized for the pressing stroke only
- Controlled decompression, without pressure shocks on the system
- Custom design for new presses and for revamping existing ones
- One supplier for both the main cylinder and the prefill valve
APPLICATIONS
Large hydraulic presses for stamping, forging, extrusion and forming, where the approach stroke is long and the main cylinder needs large volumes of oil. See also our hydraulic cylinders for presses.
Technical data
| Application | Main cylinders of large hydraulic presses |
|---|---|
| Function | Fast filling, sealing during pressing, decompression and discharge to tank |
| Pilot | Integrated hydraulic actuator for controlled opening |
| Connections | Flanges and ports defined according to the press |
| Design | Custom made, for new presses and revamping |
Frequently asked questions
What is a prefill valve for?+
It lets the main cylinder of a press fill directly from the tank during the fast approach, at high flow and low pressure. The pumps are then only needed for the pressing stroke.
When does it close and when does it open?+
It opens during the fast approach, closes when pressing begins, and is opened again by the pilot piston to decompress the cylinder and discharge the oil to the tank on the return stroke.
Can the valve be replaced on an existing press?+
Yes. Silvio Fossa S.p.A. designs custom prefill valves for revamping existing presses too, adapting flanges and ports to the installation.
Need a cylinder built around your application?
Tell us your requirements and our technical office will prepare a quote.