Atmosphere Furnace Maintenance Tips

Pneumatic Cylinders

SECO/WARWICK typically uses pneumatic cylinders for lifting and sealing doors on all types of heat treatment and melting equipment.  They may also be used to power elevators for quenches other smaller applications for mechanical transfer.

How they work

The pneumatic system uses manually or electrically operated valves to control direction of movement. Directional control valves can be operated by hand lever or electric solenoid to maintain an adjustable travel rate. The internal porting or spool of the directional control valve regulates airflow.

To extend the cylinder piston, air flows into the directional valve pressure port, through the flow control valve, and into the cylinder. As pressure builds in one end of the cylinder and the rod starts to extend, air exhausts out the opposite end of the cylinder. The flow control valve on the end of the cylinder restricts exiting airflow, which builds pressure to slow rod movement.

The exhausting air passes through the flow control valve and the directional control valve located at the end of the cylinder and exhausts to the atmosphere. When the cylinder retracts, the flow control valve at the end of the cylinder controls the flow, and the first valve allows air freely through.

Some cylinders have a cushion on one or both ends of travel.  This cushion is a flow control valve that does not operate until the cylinder piston reaches a certain point in the cylinder. Then, the cushion restricts airflow to slow the cylinder movement. This allows it to move to the end of its travel at a slower speed. This adjustment is normally on the end of the cylinder head.  See the air piping schematic to see what specific controls are provided with this equipment.

Problems to avoid

Because pneumatic systems always contain moisture from the air, the system should not be allowed to freeze. Freezing can damage the seals and control surfaces, allowing air leakage past valves, or locking a valve from operating. 

Check valves may be inserted in the line to be sure the cylinder will stay in the desired position and not drift. This is useful in case some part is leaking, or there is a loss of air pressure in the plant system.

The latest design, materials and equipment specifications should be obtained from the company before any reliance is placed on the enclosed since changes may occur due to product improvement.