What Should Be Considered When Choosing A Hard Hydraulic Tube?

Hard hydraulic tubes are an important part of the hydraulic system, used to transmit the pressure of hydraulic oil and transport various media. Hard hydraulic tubes are usually made of metal materials such as steel, copper, and aluminum, and have strong rigidity and pressure resistance.

Hard hydraulic tubes are generally composed of pipe bodies, joints, and crimping joints: the pipe body is usually made of high-strength steel and the interior is smooth to reduce pressure loss; the joint is usually made of copper alloy or stainless steel to connect the pipe body and hydraulic components; the crimping joint is used to fix the pipe to the hydraulic component.

There are many connecting hard pipes used in hydraulic systems. Once these pipes are damaged and leak oil, they will pollute the environment, affect the normal function of the system, and endanger safety. The selection, processing, and installation of hard hydraulic tubes are a very important part of the transformation of hydraulic equipment. Mastering the correct method will help the stable operation of the hydraulic system. How do we choose the right hard hydraulic tube?

Material selection

The determination of hard hydraulic tube materials depends on the specific application and should be selected according to the system pressure, flow and operating conditions:

1. Steel pipe

Medium and high pressure system piping generally uses seamless steel pipes. Due to its high strength, low price, and easy to achieve leak-free connection, it is widely used in hydraulic systems.

Ordinary hydraulic systems often use cold-drawn low-carbon steel 10, 15, and 20 seamless pipe. This steel grade can be reliably welded with various standard pipe fittings when piping.

Hydraulic servo systems often use ordinary stainless steel pipes, which are corrosion-resistant, have smooth inner and outer surfaces, and precise dimensions, but are more expensive.

2. Copper pipe

Can withstand high pressure, low price, oil resistance, corrosion resistance, good rigidity, but cannot be bent arbitrarily during assembly. It is often used as a pressure pipe in a place where it is convenient to install and disassemble.

3. Red copper pipe

Easy to bend into various shapes, but the pressure bearing pressure generally does not exceed 6.5-10MPa. It has a relatively rigid vibration resistance and is easy to oxidize the oil. It is usually used in places where it is inconvenient to connect in hydraulic devices.

Size selection

The two key dimensions of hard hydraulic tubes are outer diameter and wall thickness:

1. Inner diameter

The flow rate and flow velocity of the fluid in the hydraulic system are mainly determined by the inner diameter of the hard hydraulic tube. The inner diameter of the hard hydraulic tube is equal to the outer diameter of the hard pipe - 2x wall thickness. The unit of flow represents the amount of fluid that flows through the hard pipe line to complete the task within a specific time. The unit of flow velocity represents the speed at which the fluid flows through the hard pipe line. As the inner diameter of the hydraulic tube decreases, the flow velocity increases.

Pipeline inner diameter calculation formula: d=√(Q*K)/V

Where:

Q, flow rate per minute (L/min)

K=21.2025 (constant)

V=flow velocity (m/s)

d=oil pipe inner diameter (mm)

2. Wall thickness

The working pressure, design coefficient, and hard pipe material of the hydraulic system jointly determine the wall thickness of the hydraulic tube. The design coefficient considered when the system working pressure determines the wall thickness is 4:1, mainly considering other mechanical and hydraulic stresses that may act on the hydraulic tube when the system is working.

The standard practice in the industry is to use a design factor of 4:1 for hydraulic system design, refer to SAE J1065 and ISO 10763, and obtain the nominal reference working pressure of various steel pipe sizes.

3. Length

Cut or order the appropriate length of hard hydraulic tube according to actual needs. If the length of the hard hydraulic tube is not qualified, some problems will occur during use. If it is too long, it will be difficult to assemble it to the specified position, and if it is too short, it will be difficult to use it normally. Therefore, the length tolerance is usually set according to application requirements and customer needs, generally within plus or minus 1mm.

4. Fluid flow rate

When selecting the size of the hydraulic system hard pipe, the fluid flow rate is a major consideration. In the pressure line, higher flow rates can cause more heat generation, severe turbulence, and pressure drop. In the suction line, high flow rate fluid may cause pump cavitation.

The following maximum flow rates can be used as the initial limit values for hydraulic system design:

Pressure line: 16 ft/s

Return line: 10 ft/s

Suction line: 4 ft/s

Pressure selection

There are usually three pressure standards for hydraulic tubes: allowable working pressure, bursting pressure and explosion pressure:

1. Allowable working pressure

The maximum pressure that the hydraulic tube can withstand under normal use;

2. Bursting pressure

The minimum pressure at which the hydraulic tube may burst under abnormal use;

3. Bursting pressure

The pressure at which the hydraulic tube may explode after exceeding its maximum allowable pressure.

The maximum pressure of hard hydraulic tubes can reach more than 5000 PSI, and many manufacturers' hard hydraulic tubes will be additionally reinforced and tested to ensure that they can withstand higher pressures. In general, the bursting pressure of a hard hydraulic tube is about 4 times the pressure it withstands. When using a hard hydraulic tube, you should pay attention to the maximum pressure it withstands to avoid rupture under high pressure.

Bending radius

The bending radius of a hard hydraulic tube directly affects the mechanical properties and service life of the pipe. The bending radius standard is generally determined based on the diameter of the pipe.

Note the bending radius of a hard hydraulic tube:

1. Avoid bending radius less than the standard value

In order to maintain the performance and service life of the hydraulic tube, the bending radius should be avoided to be less than the standard value, while keeping the shape after bending not easy to deform. Generally, for hard pipes with a diameter less than 20mm, the bending radius is not less than 4 times the diameter of the pipe; for hard pipes with a diameter ≥20mm, the bending radius is not less than 5 times the diameter of the pipe.

2. Bending radius adjustment

For some special hydraulic systems with high requirements, the bending radius may need to be adjusted according to the specific situation, but it should meet the safety and durability requirements of the system.

3. Bending direction

The bending direction of the hydraulic oil pipe should avoid friction with the fixed position of the pipe or shear force after bending, otherwise it will cut the pipe or damage the internal oil seal of the pipe.

Connection method

Choose a reliable connection method, such as welding, flaring, ferrule, etc., to ensure the sealing and reliability of the pipeline.

1. Threaded connection

It is a common hard hydraulic tubeline connection method, usually used in low-pressure systems and small-size pipelines.

Vertical threaded connection (imperial thread connection): This connection is usually used for imperial pipelines, including thread types such as NPT, NPTF, PT, BSPT.

Flat sealing threaded connection (metric thread connection): This connection is usually used for metric pipelines, including thread types such as M, G, R, Rp.

2. Flange connection

Prevent leakage through the gasket seal between the two flanges, often used for the connection of high-pressure hard hydraulic tubes.

Welded flange connection: This connection is often used for large pipelines and high-pressure pipelines.

Bolted flange connection: This connection is often used for small and medium-sized pipelines.

3. Plug-in connection

The quick plug-in device can be used to quickly remove and install the pipeline without tightening the threads, making it easy to disassemble. Common plug-in connections include:

Double-cylinder connection: This connection is formed by the cooperation of two cylinders, so it is also called cylinder column connection.

Ring groove connection: This connection can make the pipeline obtain good support and sealing when plugging and unplugging.

Summary

In short, when choosing hard hydraulic tubes, we need to comprehensively consider key factors such as materials, size, pressure, bending radius and connection method to ensure safe and efficient operation of the system.