What is in this article?:
Three-head intensifier circuit with tandem cylinder
Several manufacturers produce 3-head intensifiers that eliminate external pilot-operated check valves. The first head on a 3-head intensifier has an air seal on its rod facing the air side and a hydraulic seal facing the oil side. The second head has an oil port into the rod chamber and a resilient seal facing the third head. The third head has a welded-on oil chamber that the piston rod enters. When the piston rod advances, it displaces oil from this chamber to create high pressure. The ratio of the air-piston area to the rod area intensifies the pressure by up to 40:1, or even higher. A standard 5-in. bore air cylinder with a 1-in. diameter piston rod produces 25:1 intensification. (This is a standard size for several manufacturers.) Three-head intensifiers supply a small volume of oil for short high-pressure work strokes. Calculate the high-pressure oil volume by multiplying the rod area by the stroke length after the rod passes the seal between the second and third head.
Figure 13-10 shows how 3-head intensifier C pressurizes air-oil tandem cylinder A. This circuit provides rapid low-force advance and retract strokes, with a short high-force work stroke when the cylinder meets resistance. Solenoid-operated directional valve B extends the air part of the tandem cylinder. Sequence valve D operates intensifier C. Sealed expansion tank Ereceives oil from the tandem cylinder while it extends at high pressure. For an expansion tank, mount an air filter with a clear bowl upside down, and remove the filter element. The transparent bowl makes it easy to check oil levels. This circuit eliminates air-oil tanks to make the system more compact. Figure 13-10 shows the circuit at rest.
Shifting solenoid S1 on valve B, as in Figure 13-11, makes the air-oil tandem cylinder advance rapidly to the work. Oil in the double rod-end cylinder transfers from front to back through the center head of intensifier C. (Keep these transfer lines short with oil velocity below 4 fps to minimize pressure drop.) As the cylinder advances, pressure at the cap port stays low. Adjust the spring on sequence valve D to cycle the intensifier after the tandem cylinder contacts the work.
At this contact, sequence valve D shifts to start intensifier C stroking forward, as in Figure 13-12. When the intensifier rod passes through the seal between heads 2 and 3, pressure intensification begins on the back of the double rod-end cylinder. As the tandem cylinder extends, trapped oil from the front chamber goes into expansion tank E. (Pressure increases slightly in the tank because the air trapped above the oil is compressed.) Use a tank with three to four times the volume displaced by the cylinder during the high-pressure work stroke. As the intensifier continues to stroke, increased pressure performs the work.
It is important that the intensifier contains enough oil to move the tandem cylinder through its high-pressure stroke. If the double-rod cylinder has a 3.25-in. bore with a 1.375-in. rod, and the high-pressure stroke is 0.375 in., then a minimum of 2.55 in.3 of oil is needed. Add considerations for oil compressibility plus line and cylinder tube expansion to the cylinder high-pressure stroke volume. Remember: line expansion is greater when using flexible hose. Determine the volume of oil in the high-pressure portion of the piping and cylinder, and then increase this volume by 0.5% per thousand psi of pressure. Often it requires 0.5 to 1.5 in.3 of oil at 2000 psi to make up for oil compressibility. Calculate oil compressibility and add it to the stroke volume so the intensifier does not bottom out before the oil reaches the desired high pressure. On most 3-head intensifiers, add 2.0 in. to the stroke required for volume to make up for oil that bypasses the rod before it enters the high-pressure seal between head 2 and head 3.
Figure 13-13 shows the intensifier and cylinder retracting. Deenergizing solenoid S1 on valve B lets sequence valve D spring-return to its normal condition. The intensifier starts retracting at high speed, but the tandem cylinder moves slowly. When the intensifier passes the high-pressure seal between heads 2 and 3, the tandem cylinder quickly returns to its home position.