A single-stroke intensifier produces a limited volume of high-pressure fluid. Pressure stops building when a single-stroke intensifier reaches the end of its stroke. If cylinder seals or piping leak, a single-stroke intensifier may build pressure, but then quickly lose it. When a circuit needs unlimited high-pressure volume at low flow, use a reciprocating intensifier.

Figures 13-14 through 17 show a reciprocating intensifier powering a cylinder that must hold clamping pressure for days. Reciprocating intensifier A, air-oil tank B, pilot-operated check D, solenoid valve E, and sequence valve F advance cylinder C to the work rapidly. This arrangement can hold as much as 3200 psi for long periods without wasting energy or generating heat.

Fig 13-14











Several companies assemble reciprocating intensifiers with a directional valve, limit valves, and check valves in a unit. Special-order units may come with air-oil tanks, special valves, or accumulators — all pre-piped for operation. When supplied with pressurized air, the unit in Figure 13-14 cycles and pumps oil until it reaches a maximum pressure. Other units operate from a pilot signal whenever the machine requires intensified pressure. For even higher pressures, dual or triple air pistons give higher ratios. Double-acting intensifiers increase oil volume while using less air. Most manufacturers offer single-acting intensifiers as standard and double-acting intensifiers as an option. When a machine needs a low to medium volume of high-pressure oil and has long holding times, use a reciprocating intensifier.

Fig 13-15











The circuit changes as shown in Figure 13-15 after the cylinder contacts the work. The intensifier starts cycling because pressure buildup shifts sequence valve F to open. Pilot-operated check valve D closes, blocking pressure fluid from going to tank. Pressure in cylinder C is already at 800 psi. As the intensifier retracts, suction draws oil in through the right-hand check valve to fill the oil chamber. Its spring and the pressure already in the work cylinder hold the left-hand check valve closed. A reciprocating intensifier is a low-volume, single-piston, pressure-compensated pump that continues to move fluid until it reaches maximum pressure. Because output from the intensifier is intermittent, cylinder movement is jerky, as is the rate of pressure increase.

Fig 13-16











Figure 13-16 shows the intensifier changing from filling mode to pumping mode. The reciprocating air piston depresses the upper cam valve, reducing pressure on the right end of the double-bleed valve and causing it to shift. Both check valves close at this time, trapping oil in the cylinder. The intensifier now starts its pumping stroke.

Fig 13-17











The intensifier is extending and discharging fluid through the left check valve to the actuator in Figure 13-17. Fluid fills the actuator and pressure increases. The intensifier continues to reciprocate until it reaches maximum pressure. At maximum pressure, the intensifier stalls but continues to make up for internal or external leakage.

With the addition of an accumulator, a reciprocating intensifier could supply cylinders or motors that operate intermittently. The accumulator stores oil during machine idle time, and then discharges it at high flow without pulses for short periods. Use flow controls to slow the rapid uncontrolled movements likely to occur when using an accumulator.