Hydraulic Basics

Starting off a project that needs hydraulics tools? Before you get a Stanley Hydraulics tool from BST Group, here are some basic pointers as a refresher. (30min read)

The Hydraulic Principle

The basic principle of hydraulics used for tool operation can be compared with a typical rotary car-wash brush tool, that is operated from water through a garden hose. Water rushing through the garden hose drives a small motor in the car-wash tool which, in turn, rotates the brush.

However, it is not just the rushing water that is driving the motor. There is also pressure associated with the rushing water—about 60 pounds per square inch (psi). Without the pressure, the tool would have no power. Without pressure, any force applied to the tool, such as pushing down on the tool, would stall the tool. Water rushing through the hose (or the flow of water) is measured in gallons per minute (gpm) and results in the speed of the tool (in the case of the car-wash tool, the speed of the brush). Pressure associated with the water provides power to the tool.

The same principle applies in one of our tools. In a breaker, for example, the flow results in the speed of the tool and the resistance to that flow creates a demand for pressure. If the system has the capacity to deliver the pressure, power is transmitted to the tool to do work. Hydraulic tools actually use less flow (gpm) than that produced through a garden hose. The pressure, however, is considerably higher. Hydraulic tools require pressures up to 2000 psi / 140 bar but only need 5 to 10 gpm to operate effectively. A typical HTMA hydraulic system returns fluid to a reservoir for re-use as opposed to the car-wash brush tool that spills fluid to waste.

In pictures, the priciple of hydraulics looks like this:

Pressure exerted on a fluid is distributed equally throughout the fluid (Pascal’s Principle). Hydraulics uses incompresible liquids so the applied pressure from one end (smaller arrow) is equal to the desired pressure on the other end (bigger arrow). The bigger arrow is pointing towards a piston that is free to move (it can also be connected to a rod). When the force is applied, the piston moves up and down.

Open & Closed Center Systems

Open Center Systems

Closed Center Systems

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.

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 handheld 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 Do’s & Don’ts For Cool Oil Control

• DON’T rely on a large reservoir to control oil heating. Large reservoirs, even with good air circulation, do not adequately dissipate heat.
• 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.
• 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.
• DON’T use heavy oils such as 30W or 10W30 engine oils. These will cause resistance in lines and add to backpressure and heat. Refer to Recommended Hydraulic Fluids for more details.
• DON’T run return oil through control valves or other circuit components, except coolers and return line filters.

Reducing Heat Generation

• DO 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.
• DO use generous line sizes — Especially on pump suction and return from tool to tank.
• DO use oils in 130-225 SSU at l00° F / 38° C range with high viscosity index.

Providing Good Cooling For Hydraulic Oil

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. Don’t use “thermal” viscous-drive fan because these fans do not draw air unless the engine is hot. 

Flow Controls

Flow Control Valves

These valves regulate the flow rate of hydraulic fluid in a system. They come in various types, including:

a. Throttle Valves: Throttle valves create a constriction in the flow path, resulting in a controlled flow rate. By adjusting the valve opening, operators can regulate the fluid velocity and, consequently, the flow rate. Throttle valves are commonly used in applications where precise speed control is necessary, such as hydraulic cylinders and motor drives.

b. Pressure Compensated Flow Control Valves: These valves maintain a constant flow rate regardless of variations in system pressure. By utilizing a pressure compensator mechanism, these valves automatically adjust the flow rate to maintain a consistent output, making them suitable for applications where consistent actuator speed is crucial.

Flow Dividers

Flow dividers distribute a single input flow into multiple output flows with specific flow rates. They are commonly used in applications where hydraulic power needs to be evenly distributed among multiple actuators, such as in agricultural machinery or material handling equipment. They ensure that each actuator receives an appropriate share of the total hydraulic flow.

Flow Regulators

Flow regulators control the flow rate to a specific maximum value. They are often used in applications where excessive flow can lead to system damage or inefficiency. Flow regulators help maintain a consistent flow rate within a given range, ensuring optimal performance and protecting the system components.

Proportional Flow Controls

Proportional flow controls enable precise control of the flow rate by adjusting the valve opening in proportion to an input signal. These valves are commonly used in applications that require dynamic and accurate control, such as industrial automation, robotics, and machine tools.

Check Valves

While not directly controlling the flow rate, check valves play a crucial role in maintaining the desired direction of flow. They allow fluid flow in one direction while preventing reverse flow. Check valves are essential in hydraulic systems to ensure proper functioning and prevent damage due to backflow.

Quick Disconnects

Quick disconnects allow for rapid and straightforward attachment and detachment of hydraulic hoses, enabling users to swiftly switch between different tools and equipment without the need for time-consuming manual connections. With Stanley Hydraulic advanced quick disconnectors, operators can maximise uptime, reduce downtime during tool changes, and ensure seamless operations in demanding environments. Whether in construction, mining or other heavy duty industries, Stanley Hydraulic Tools’ quick disconnects play a crucial role in simplifying hydraulic connections and providing users with a dependable solution for their operational needs.

Hose Types

1. High Pressure Rubber Hoses
   • Excellent pressure resistance for demanding applications
   • Robust construction ensures durability and longevity
   • Ideal for heavy machinery, construction equipment and industrial use
2. Thermoplastic Hoses
   • Lightweight and highly flexible, allowing easy handling and installation
   • Superior abrasion resistance for extended service life
   • Resistant to chemicals and oils, suitable for diverse industries like agriculture and aerospace
3. Stainless Steel Hoses
   • Exceptional corrosion resistance, making them ideal for corrosive environments
   • Capable of withstanding extreme temperatures and harsh conditions
   • Well suited for marine, chemical processing and offshore applications
4. Spiral Wire Hoses
   • Multiple layers of steel wire provide high tensile strength and pressure resistance
   • Ensures reliable performance in heavy duty applications
   • Widely used in construction, mining and drilling industries
5. Braided Hoses
   • Strikes a balance between strength and flexibility
   • Ideal for automotive and mobile machinery applications
   • Offers good resistance to pressure and handling stress