Question: The stroke of the cylinders in Problem is 18 ft. The design states that the truck must be lowered in 10 min. The counterbalance valve is a cartridge mounted in an aluminum block known as a line body. Total mass of the counterbalance valve is 9.4 lb. The pressure setting of the valve (inlet pressure) is 2200 psi, and the pressure drop from the outlet to the reservoir is 50 psi. Use the following assumptions and calculate the temperature rise of the counterbalance valve during a retraction event.
a. The valve is mounted on the cylinder. 20% of the total heat generated is conducted to the cylinder.
b. 40% of the total heat generated is exchanged to the oil as it passes through the valve.
c. 30% of the total heat is convected or radiated to the surrounding atmosphere during the event.
Problem: A peanut shelling plant uses a truck dump to unload truck-trailers loaded with peanuts. The truck is backed onto a platform, and the entire vehicle (tractor and trailer) is raised to pour the peanuts out through the back unloading gate. The hose on the cap end of one lift cylinder failed at the fitting, and this caused the entire load to be held by the other cylinder. The resulting high pressure caused the hose on this cylinder to burst, and a $105,000 truck was destroyed. You are assigned the task of redesigning the hydraulic circuit such that a similar accident could never happen again. Your circuit is shown in Fig. A counterbalance valve is installed directly on the cap end port of the cylinder. There is no line (hose or hydraulic tubing) between the port and the valve. For simplicity, there is only one cylinder shown. The actual design has two cylinders with a counterbalance valve on each one.
Given: Cylinders 8-in. bore
5-in. rod diameter
Maximum lift force 10 tons
a. Find the setting on the counterbalance valve (psi) that will ensure that the load can never fall. Valve setting should be 10% higher than the pressure produced by the expected maximum load.
b. What pressure must be developed at the rod end of the cylinder to lower the load?