CEB Press/Research Development/Hydraulic Design

Hydraulic System Design of CEB

Overview

The CEB contains three hydraulic circuits each operating a single actuator

• Main Cylinder, which compresses the earth
  This circuit is controlled by a 4-way solenoid valve which can raise, lower, or hold the cylinder in position, based on whether the A coil, B coil, or neither coil is energized.
• Secondary Cylinder, which operates the drawer
  This circuit is controlled by a 4-way solenoid valve which can retract, advance, or hold the cylinder in position, based on whether the A coil, B coil, or neither coil is energized.
• Shaker Motor, which vibrates the hopper
  This circuit is controlled by a 4-way solenoid valve, however only the A coil is used in this design; when energized the motor rotates.

The circuits are arranged in an open-center, series configuration: when no circuits are active, the hydraulic fluid flows freely through the three "open centers" of the valves and returns to the power unit. If a valve is actuated, the fluid flows to that actuator and returns to the power unit.

It is also possible to actuate two valves at the same time (e.g. for Main Cylinder and Secondary Cylinder); in this situation the fluid leaving the Main Cylinder runs "in series" to the Secondary Cylinder circuit, and both pistons move simultaneously.

Circuit Diagram

(Source file: File:CEB Hydraulic.ppt,using Hydraulic_Symbol_Library)

Circuit Description

Main Cylinder Circuit

The A and B ports of the 4-way valve are routed directly to the bottom and top ports of the cylinder.

Secondary Cylinder Circuit

The secondary cylinder circuit includes a pressure-compensated flow control valve which limits the advance speed of the drawer. When valve port B is pressurized (cylinder advance), fluid flows through the flow control valve to the cylinder at the set flow rate, while excess fluid passes through the check valve and returns to the power unit.

When valve port A is pressurized (cylinder retract), fluid flows directly to the front port of the cylinder. Fluid returns from the back port of the cylinder through the restriction in the flow control valve (not pressure compensated, so higher flow?) to the power unit.

The flow control valve incorporates an internal relief valve which limits the force applied on the advance stroke.

Shaker Motor Circuit

Unlike the cylinder circuits, this is a unidirectional circuit. When valve port A is pressurized, fluid flows through the motor and returns through the needle valve, which sets the flow rate and therefore the rpm of the motor.

Note that, unlike the cylinder circuits, this circuit uses a full-open-center valve which allows the motor to freewheel after the valve is de-energized; this limits pressure surges which might otherwise occur.

The motor case drain port is tee'd into the return line going to valve port B.

Design comments

Shaker Motor Circuit

• The case drain connection is unnecessary, as the motor has internal check valves which route case drain to whichever main port is at lower pressure.
• Placing the needle valve in the return line causes the return pressure to be high during operation, which is stressful to the shaft seal. Consider moving the needle valve to the inlet side of the motor.

Overall

There doesn't seem to be an overall relief valve in the system; can we rely on the powercube to have pressure limiting relief? Otherwise pressures could soar when pistons reach end of travel (except at end of drawer advance, where the flow control's internal relief acts). Perhaps use Daman AD05S033S/C manifold with C-10-2 cartridge relief valve.

Design computations

TBD: Pressures, forces, flowrates, power consumption, etc. Similar to earlier version (CEB_Design)

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From Liberator v1.0 spec sheet

• Supply pressure: 2300psi operating
• Supply flow: 24gpm rated, 28gpm max
• Main cylinder: 5in dia bore, 2in dia rod, 8in full stroke
• Secondary cylinder: 2.5in dia bore, 1.25in dia rod, 14 in full stroke

Main cylinder piston area = π/4 * d^2 = π/4 * (5in)^2 = 19.6in^2
Brick compression force = P*A = 2300psi * 19.6in^2 = 45080lbf
Brick compression chamber pressure = F/A = 45080lbf/(6in * 12in) = 626psi

Main cylinder rising speed = Q/A = 24gpm * 231in^3/gal / 19.6in^2 = 283in/min = 4.7in/sec

Main cylinder rod area = π/4 * d^2 = π/4 * (2in)^2 = 3.1in^2
Main cylinder net area (rod side) = A1 - A2 = 19.6in^2 - 3.1in^2 = 13.5in^2
Main cylinder descent speed = Q/A = 24gpm * 231in^3/gal / 13.5in^2 = 410 in/min = 6.8in/sec