Dual-output pump helps keep excavator compact
Mustang Mfg Co., West Bend, Wis., has focused on compact excavators for the past several years. Four new models bring the number of excavators to 12 in their compact line, which extends in size from 1.5 to 12 metric tons.
In the Mustang ME 3503 excavator, one of the newer models, a Kubota D1703 diesel engine — with an output rating of 32.6 hp at 2450 rpm — drives a 3000-psi Nachi PVD 1B pump via a coupler. This pressure-compensated pump incorporates a conventional variable-displacement 10-piston rotating group, but has a special port plate configuration that splits outlet flow into two equal sections — with less than 1% variation — to supply circuits P1 and P2. The combined flow rate is 20.7 gpm. Also included in the ME 3503 hydraulic package is a rear-mounted gear pump with a flow rate of 6.8 gpm that supplies circuit P3. Thus, the excavator's total available flow is 27.5 gpm.
Circuit P1 operates the left travel motor, bucket, and boom functions. Circuit P2 operates the right travel motor, arm, and independent boom swing. Circuit P3 operates the swing, dozer blade, and counterbalance functions. In addition, a flow-control section in the main control valve can combines flow from P2 and P3 to operate the auxiliary hydraulics. This arrangement allows the operator to adjust flow to match attachment requirements. It can be adjusted from a combined flow of 17.2 gpm to a individual flow of 10.4 gpm. Thus, the hydraulic system allows for a high flow auxiliary circuit and very effective use of all other machine functions.
Excavator functions are activated by a 500-psi pilot circuit. (The auxiliary hydraulics-section, which is cable controlled via a foot pedal, is the only function-not activated by pilot oil.) The operator uses joysticks or electrical switches located on the joystick-levers to directs pilot oil to the main control valve or switch valves to control a function.
The operator controls the travel system via two foot pedals (with levers). They receive pilot oil from the pilot control unit and are fitted with orifices to reduce the flow, thus dampening the travel and providing smooth acceleration. Mustang provides two methods of changing the travel speed of the machine. One is a push button located on the right travel lever (which must be held depressed by the operator); the other is a toggle switch on the dashboard. With either method, an electrical signal energizes a solenoid valve that diverts pilot oil to both travel motors. The pilot-oil pressure changes the angle of both motor swashplates to increase travel speed. The operator can depress the push button for short bursts of high speed as required. If the excavator is traveling a long distance, the dashboard switch can be activated to maintain high speed.
When P1 and P2 are both delivering oil to the travel circuits (for straight travel), the counterbalancing section of the main control valve is activated. This allows oil from P3 to enter into the P1 and P2 sections of the main control valve. P3 oil then can operate the boom, bucket, arm, swing, or dozer functions, while the machine travels.
Two joysticks — ergonomicallyplaced with comfortable arm rests — are used to control the swing, boom, arm, and bucket circuits. (The control pattern can easily be changed from ISO to SAE controls by turning a lever on the switch valve located under the floor mat.) Located on the right joystick are two buttons. One sounds the horn, the other activates the dozer blade. When the second button is pushed, an electrical signal is sent to shift the dozer switch-over valve. This diverts oil from the boom circuit to the dozer cylinder. The operator simply holds the button in and moves the joystick fore or aft to position the dozer blade.
A foot pedal activates the auxiliary circuit for optional attachments. When the optional attachment is a single-acting system, such as a hydraulic hammer, a manually operated valve is provided to direct the return oil directly back through the oil cooler to the tank. The same foot pedal also activates the independent boom swing. When the operator depresses a button located on the left joystick, he energizes a solenoid that diverts oil at a switch-over valve from the auxiliary circuit to the independent boom swing.
Contact Mustang Mfg. at (262) 334-9461 or visit www.mustangmfg.com.