Handheld Tool Catalog

33 HANDHELD TOOLS www.stanleyinfrastructure.com 800-972-2647 OPEN-CENTER AND CLOSED-CENTER SYSTEMS There are two basic types of hydraulic systems — Open-Center and Closed-Center. OPEN-CENTER IS CONSTANT FLOW — VARIABLE PRESSURE When a tool valve is in the OFF position, hydraulic oil flows through the ON/OFF valve ports of the tool and back to the reservoir. The system is constantly flowing oil through the tool valve ports and back to the reservoir at no pressure. When the tool valve is ON, oil circulates through the tool causing the tool to operate, and then returns to the reservoir. Pressure is created when resistance to flow is sensed by the system. This occurs when the tool is put to work. Pressure will increase as the tool needs it up to the relief setting in the hydraulic system. CLOSED-CENTER IS CONSTANT PRESSURE — VARIABLE FLOW When a tool valve is in the OFF position, hydraulic oil flow stops at the ON/ OFF valve port of the tool. The system will build and hold pressure without returning oil to the reservoir. When the tool valve is ON, oil circulates through the tool causing the tool to operate, and then returns to the reservoir. Pressure tends to be constant in the system. Pressure will increase as the tool needs it up to the settings in the hydraulic system. And if pressures higher than the system setting are demanded by the work, flow will decrease. FLUID TEMPERATURE The following information will serve to assist those installing hydraulics in mobile applications for hand held tools. While many hydraulic circuits can run upwards to 200° F / 93° C, temperatures over 110° F / 43° C are uncomfortable to human touch. Our desire is to hold oil temperature to a maximum of 140° F / 43° C. In almost any hydraulic tool circuit, oil cooling methods will be required except for very short periods of operation or in underwater and extreme cold environments. If you are involved in the design of a hydraulic tool circuit, use the following as guidelines. BASIC DON’TS FOR COOL OIL CONTROL 1. DON’T — Rely on a large reservoir to control oil heating. Large reservoirs, even with good air circulation, do not adequately dissipate heat. 2. DON’T — Set relief pressure too low (open-center circuits) for percussion type tools (breakers, hammer drills, etc.). Pressure peaks may run up to 350 PSI over gauge pressure, popping the relief and causing heat as well as low tool performance. 3. DON’T — Pump more oil than the tool should use and avoid flow controls if possible. Instead, size the pump for desired flow volume. Gear type flow dividers can be used to reduce flow more efficiently than valves, reducing heat. 4. DON’T — Use heavy oils such as 30W or 10W30 engine oils. These will cause resistance in lines and add to back pressure and heat. 5. DON’T — Run return oil through control valves or other circuit components, except coolers and return line filters. DO THE FOLLOWING TO REDUCE HEAT GENERATION 1. Operate pumps at moderate speed — gear pumps usually generate less heat and are less prone to cavitation at speeds of 1,000-2,000 RPM. 2. Use generous line sizes — Especially on pump suction and return from tool to tank. 3. Use oils in 130-225 SSU at l00° F / 38° C range with high viscosity index. (see hydraulic fluid recommendations at the end of this section) PROVIDE GOOD COOLING FOR HYDRAULIC OIL 1. Use an air-to-oil cooler of maximum size for space available. Use a shrouded, high capacity fan. Many vehicles do not cool well when parked with engine at low speed. Do NOT use a “thermal” viscous-drive fan because these fans do not draw air unless the engine is hot. FLOW CONTROLS 1. General Notes — To reduce or control flow rate through STANLEY Tools, flow control valves are sometimes necessary. All possible effort should be made to avoid use of flow control valves where appropriate pump volume can be used because: A. Excess oil volume and subsequent pressure drop generates heat. B. When percussion type tools that generate pressure pulses are used, flow controls may oscillate and cause flow changes which reduce tool performance and add increased heating. 2. Flow Control of Open-Center Circuits — Always use a priority type pressure-compensated flow control. This will prevent relief popping and reduce heat build-up. The excess flow should be routed in an unrestricted manner to the reservoir. 3. Flow Control of Closed-Center Circuits — Use a two-port, pressure- compensated flow control. Some of these are very compact, in the range of 1-1/4” diameter by 5” long, and can be attached to the tool pressure pigtail. Do not use priority type controls on closed-center circuits, as this will cause the pump to operate at full volume — further heating the oil. QUICK DISCONNECTS 1. Only use quick disconnects matching hose diameters. i.e. 1/2 inch port quick disconnect for 1/2 inch inside diameter hose. 2. Use as few quick disconnects as possible and avoid using adapter fittings with quick disconnects. Fittings and quick disconnects, while necessary, create flow restriction which causes heat and reduced tool performance. 3. Always use HTMA recommended quick disconnects that are flush-faced and drip less. HYDRAULIC BASICS