Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads Custom Inline Archive Www hydraulicspneumatics com Content Site200 Articles 09 01 1993 85202 Pedalmovem 00000057533
Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads Custom Inline Archive Www hydraulicspneumatics com Content Site200 Articles 09 01 1993 85202 Pedalmovem 00000057533
Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads Custom Inline Archive Www hydraulicspneumatics com Content Site200 Articles 09 01 1993 85202 Pedalmovem 00000057533
Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads Custom Inline Archive Www hydraulicspneumatics com Content Site200 Articles 09 01 1993 85202 Pedalmovem 00000057533
Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads Custom Inline Archive Www hydraulicspneumatics com Content Site200 Articles 09 01 1993 85202 Pedalmovem 00000057533

Staged modulation improves forklift brake control

Sept. 1, 1993
Pedal movement provides low-pressure braking for maneuverability, or high-pressure braking for fast, safe stops. Taylor Model TE-155S 80-hp diesel-powered forklift has more than 71/2-ton lift capacity and almost 15-mph ...
Pedal movement provides low-pressure braking for maneuverability, or high-pressure braking for fast, safe stops.
Taylor Model TE-155S 80-hp diesel-powered forklift has more than 71/2-ton lift capacity and almost 15-mph travel speed. Pedal-operated staged-modulation of hydraulic brake system helps operators safely maximize performance.
Pictured below are two versions of rugged ductile-iron 1100 Series modulating brake valves: suspended pedal, at left, and treadle, at right. Simplified schematic diagram at immediate left shows typical arrangement when connected for tandem braking circuit.

When a forklift operator makes an approach to pick up or stack a load. cont trof the movement of the forks is obviously critical to speed and accuracy. Lessobvious, but equally as important, is control of the vehicle’s braking system Forklift builder Taylor Machine Works, Inc., Louisville, Miss., installs staged-modulation hydraulic brake Ives from Carlisle Braking System in their equipment to help operators maximize performance.

Staged modulation in a hydraulic brake System provides a non linear pressure rise in response to pedal motion. As the vehicle operator first depresses the brake pedal, brake pressure rises gradually in response to pedal position, making it very easy to control When high brake pressure is requlred, depressing the pedal farther brings a rapid rise in brake pressure. Typlcally, the vehicle operator brakes with low pressure most of the time Full-pressure stops are made only rarely generally under panic conditions. In either case, the valve spring-returns.

Carlisle Braking Systems, Bloomington, Ind accomplishes staging by putting dual-rate pressure-regulating springs in their modulating control valves The rate of pressure rise is predetermined in both the lower and upper portions of the plot shown above by sring selection at the factory. The transition point between the upper and lower plots may be field-adjusted by turning an external screw located under the pedal. These changes can be made without disassembling the umt, and the screw is locked in place once the transition point is set. Carlisle has offered the staging option in the past only in their high-end 2100 Series modulating control valves used on large wheel loaders and haulage trucks. By adding the staging option to the more economical 1100 Series, Carlisle brings smooth modulation to valves suitable for forklift truck and small wheel loaders. The highflow 1100 Series may be used in open-center, closed-center, and load-sensing hydraulic systems, and models are offered for single and tandem circuits. Its dampedspool design provides noise-free modulation across the range of all output pressures.

For a typical tandem braking circuit, as dlagrammed at right, the pressure source is a dedicated pump or an accumulator. With the modulating valve at rest, pressure to both circuits is blocked and return lines from the brakes are connected to tank. When the operator depresses the pedal, the valve shifts quickly through the all-ports-blocked center position and then begins to pass flow to the brake circuits. As brake pressure increases, the pilot forces developed in opposition to the pedal force eventually take command of the spool and shift it to its center position, locking that level of pressure in the brake circuits. When the operator releases the pedal, spring and pilot forces combine to return both spools to their original positions.

Series 1100 valves are designed with larger internal passages and contours that limit flow forces. The resulting high flow capability reduces brake reaction time and shortens stopping distance— particularly when used for wet brakes with large displacements (an industry trend today)

Options for the modulating valves include: treadle pedal actuation, automotive- style suspended pedal for firewall- mounting, horizontally mounted valves with treadle pedal for constrained space, hydraulic or pneumatic pilot supply, and adjustable proximity switches for stop-light actuation.

Phil Redenbarger. section manager product development, Carlisle Off- Highway Braking Systems. describrd the operation of this component.

About the Author

Richard Schneider | Contributing Editor

Contributing Editor, has been affiliated with Hydraulics & Pneumatics for more than 30 years and served as chief editor from 1987 through 2000. He received a BSME from Cornell University and also completed additional courses at the Milwaukee School of Engineering. His diverse background in industry includes ten years with a fluid power distributor and a variety of other professional positions. He has also been active with the National Fluid Power Association and Fluid Power Society.

Continue Reading

Motor leakage variations

Oct. 18, 2006
affect low-speed performance

The Impacts of Electrification on Fluid Power Systems

May 15, 2023
Electrification presents challenges as well as opportunities to re-evaluate and improve upon the design of hydraulics and pneumatics.

Sponsored Recommendations

7 Key Considerations for Selecting a Medical Pump

Feb. 6, 2024
Newcomers to medical device design may think pressure and flow rate are sufficient parameters whenselecting a pump. While this may be true in some industrial applications, medical...

How Variable Volume Pumps Work

Feb. 6, 2024
Variable volume pumps, also known as precision dispense pumps, are a positive displacement pump that operates by retracting a piston to aspirate a fluid and then extending the...

What is a Check Valve and How Does it Work?

Feb. 6, 2024
Acheck valve, a non-return or one-way valve, is a mechanical device that allows a gas or liquid to flow freely in one direction while preventing reverse flow in the opposite ...

The Difference Between Calibrated Orifices and Holes

Feb. 6, 2024
Engineers tasked with managing fluid flow talk about both holes and calibrated orifices, but they are two distinct entities. A hole can be any opening, but a calibrated orifice...