When I teach hydraulic troubleshooting classes, I always ask my students, “If a cylinder does not move when I shift the directional valve, is it a pressure problem or a flow problem?”.
Most of the students will say it is a flow problem. Then I ask them, “But what if I don’t have enough pressure to move the load?”
If the actuator does not move, I always think to myself, “why don’t I have enough pressure to make it move?". Something is taking my flow elsewhere at a lower pressure. Or, if it’s moving slower than it should I think, "Why don’t I have enough flow? Where is part of my flow going where it shouldn’t?”.
A scrap yard had a metal compactor that is fed by a large metal shredding machine driven by a 1500 HP electric motor. The compactor had a 3-bank series manifold with DO5 directional valves incorporating A & B meter-out flow controls. Circuit reliefs were used on all the A & B lines to protect the vane pumps and reduce energy consumption. Only one circuit at a time would be engaged during operation and each function would operate at a different pressure. The PLC program was checked and verified that all the interlocks would only let one function operate at a time. The lowest relief valve was set at 600 psi while the highest relieved...
A plating mill receives 6-8 ft. wide coiled steel and chemically treats it with a process similar to galvanizing. The rolls have about a 4-6 ft. OD and are unraveled like paper towels. The loose end of a sheet is fed into a pair of pinch rolls that direct the steel through several stations that wash, rinse, dry, and heat it. After it is coated and treated, the steel is then rolled back into 4-6 ft. coils and shipped to automotive stamping plants. An impressive mill like thid can be a city block long.
Feeding a new sheet into the pinch rolls and subsequent stations is time consuming. To reduce this bottleneck, plant pe...
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...
An automotive company built an assembly plant on land that had a limestone base. Research found that if the limestone was removed, crushed and re-laid, the plant stability and harmonics would be improved to a point that would offset the cost of crushing the limestone.
They used a large rock crusher that had a fairly simple hydraulic circuit. Two Caterpillar front end loaders would dump large chunks of broken limestone into a chute from either side of the rock crusher. A mechanical vibrator would move the limestone down to a large rotating drum with 50 to 60 swinging hammers that would pulverize the limestone into stones no larger than...
As the economy started improving after the recent downturn, several hydraulic distributors were adding new people that sometimes got in over their head designing circuits for their customers. We received a call from a new salesman asking for our help in solving problems he was having with a system he designed and installed. He sent the circuit (shown below) to us for review and comment. The problems he was experiencing were as follows:
When debugging the system, the customer blew a 25 gpm spin-on filter element off its filter head. He bypassed it for the time being.
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...