An automotive assembly plant installed a simple two speed circuit, to advance a hydraulically driven cylinder at high speed, and shift to a slower speed for pressing. (See figure below, which the maintenance supervisor used for plumbing.)
Plant personnel were experiencing problems with the alignment of the steel stamping being out of line with the bored hole in the casting when shifting into slow speed. Shifting the 2-position directional valve to the slow pressing speed triggered a “bump” or “jolt” causing unwanted movement of the stamping.
In a recent hydraulic class, they were taught that fast shifting directional valves can cause s...
A company that makes all types of fireplaces and chimneys had a new press fabricated for forming top covers for chimneys. This press was built to handle all the custom designs requested by architects and builders. The tops, called chase covers, were normally made from SAE 304 stainless steel of various thicknesses. The press was inspected as it came out of the fabrication shop. After its speed and tonnage were confirmed, it was shipped to the customer’s assembly plant. The customer fitted the press with clamping and forming fixtures and began the fine tuning process of making good parts.
Controlling a run-away load with meter-out flow controls normally causes intensified pressure on the rod side of the cylinder if the load is trying to extend the cylinder.
Taking the area ratio of the cylinder, (cap end area divided by the rod end donut area), multiplied by the system pressure on the cap end, will give the rod area pressure. An example would be a 3:1 area ratio, times a system pressure of 2000 PSI, resulting in 6000 PSI (PLUS what the load would add). See Fig. A.
Proper design would use a counterbalance valve with a meter-in flow control as shown in Fig. B. This will result in the rod pressure only being a...