Hydraulic tube assembly design: routing, bends and fitting access

1. Define tube requirements within the hydraulic system design

Start with the approved operating conditions and interfaces. Hydraulic component design determines what a component must do; tube assembly design determines how the specified connections can be reached, manufactured and inspected.

Translate operating requirements into tube inputs

Record the fluid, operating pressure and temperature conditions, along with any pressure peaks or movement the system designer requires you to consider. Keep these separate from a machine's processing range. A bender's diameter range does not establish a tube assembly's pressure rating or the bore needed for the circuit.

ISO 4413 covers hydraulic system design as well as assembly, installation, maintenance and cleaning. That scope is a useful reminder to review the tube throughout its intended use, rather than only in its fitted position. [1]

Define the installation envelope, not just the finished outline

Include the path used to insert and remove the tube, the space needed to assemble its ends, and nearby components' movement. For a custom hydraulic system, confirm which interfaces are fixed before optimizing the route around them. A later port change can invalidate otherwise correct bends.

2. Match the tube, fittings and fabrication tools

Treat the tube, connection and tooling as one combination. Record the material and wall thickness beside the outside diameter, then identify the fitting series and the tools required for that connection.

Different connection systems need different preparation

Our rigid pipe hydraulic fittings include 24° bite-type, 37° flare and weldable configurations. These are different connection methods, not alternative names for the same tube end.

ISO 8434-1:2018 addresses 24° cone connectors, including cutting ring and DKO designs. ISO 8434-2:2007 addresses 37° flared connectors. Identify the applicable connection specification and edition; a shared tube diameter does not establish interchangeability between these systems. [2] [3]

A diameter range is a starting filter

The XYOON KC-K01 memory pipe bending machine and KC-A01 electric cutting ring pre-assembly flaring machine cover a 6 to 42 mm tube diameter range. That shared range is useful for shortlisting equipment. It does not confirm the required bend radius, wall thickness, connection tooling or access for a particular finished part.

Before release, pair each tube specification with its bend die and connection tool. Include tool identities in the part record so that a change of die or fitting series triggers a review rather than an unnoticed substitution.

3. Plan tube routing for compact and mobile equipment

Review the route in the order the machine will be assembled and serviced. The final tube outline is only one part of that check; the insertion path, surrounding movement and tool access also need space.

Separate fixed routes from moving interfaces

For hydraulic systems for mobile equipment, identify which components move relative to each other. Do not treat a rigid tube spanning such an interface as a routine fixed connection. Resolve the movement with the system designer and the applicable connection arrangement.

Mark mounting points and moving-part envelopes on the same installation model. Keep the proposed route clear of those envelopes throughout the required motion. Review support locations with the installation design; a generic clamp spacing copied from a different tube or duty is not a substitute.

Check access even when the system is small

A small hydraulic system can leave very little room around a valve block. Check how the tube enters, where the wrench approaches and whether a neighboring component must be removed first. Record an unavoidable removal dependency in the assembly instructions rather than leaving the installer to discover it.

Use a bend when the available tooling can produce the route and retain usable ends. Consider an elbow or separable section when it resolves a defined access problem. Compare the complete arrangement, including additional connections and the assembly sequence, instead of assuming the fewest fittings always gives the most practical result.

4. Choose bend radii that match the tube and tooling

Specify the centerline bend radius and check it against the actual tube and die. A radius that fits the installation is not automatically a radius the selected setup can form acceptably.

A larger radius can consume the connection straight

Hold the tube end and the theoretical corner fixed, then increase the radius. The bend starts earlier along the incoming leg, leaving less straight tube at the connection. That geometric trade-off is easy to miss when reviewing only the space around the curved section.

For a simple circular bend with direction change θ between 0° and 180°, the tangent setback is R × tan(θ/2). If A is measured from the tube end plane to the theoretical corner along the incoming centerline:

For a geometry example, assume A = 65 mm and a 90° bend. A 30 mm centerline radius leaves 35 mm straight. Increasing the radius to 45 mm leaves 20 mm: 15 mm less connection straight, even though the end and theoretical corner have not moved.

These assumed dimensions illustrate geometry, not an approved tube specification. Compare the resulting straight with the exact fitting and tooling requirements. The calculation does not establish bendability, an allowable wall thickness, springback compensation or the cut length of the blank.

Confirm the formed section as well as the radius

Inspect the trial bend against the drawing's requirements for angle, cross-section and surface condition. If the selected radius or tube changes, revisit the connection ends and the remaining bend sequence. Do not approve the change from a radius number alone.

5. Reserve straight ends and fitting tool clearance

Start a fabrication review at the two ends of the tube. Check that the hardware can be loaded and that the preassembly tool and final wrench can approach. Then examine the bends between those ends.

If the last bend sits close to a connection, changing the angle alone may not solve the problem. Check the remaining straight, the grip location and the operation order. Compare moving the bend, changing the connection arrangement or dividing the assembly. Do not use the fitting nut to pull a misaligned tube into position.

Give each operation its own space check

Do not turn several clearances into one guessed dimension

Some requirements act along the tube; others require radial access or a tool sweep. Adding them all into a single straight-length allowance can hide the actual interference. Record both the required straight length and the relevant approach envelope.

Obtain dimensional requirements from the matching fitting and tool information. If access still needs confirmation, use the actual tooling and a representative part before releasing the drawing. Nominal outside diameter alone is not enough to specify a universal minimum straight.

6. Define datums, rotation and bend sequence

A multi-bend tube needs more than a list of angles. Define the reference end, the locations of bends and the rotation between bend planes. Two parts can have the same bend angles yet finish with different end positions or directions.

State how the tube is viewed

Mark datum A and the viewing direction used to describe rotation. Identify whether a distance refers to a tangent, theoretical corner or another drawing feature. A bare list of numbers leaves too much room for different interpretations.

Review the next bend before making the current one

Check whether an earlier bend blocks the next grip location, the workpiece's rotation or tool withdrawal. A sequence that works on an unbent blank may become inaccessible once a leg has been formed.

The KC-K01 uses angle memory and compensation settings. Those features help manage repeated bend settings, but they do not define the tube's axial locations or rotation references. Keep the drawing revision, tooling and relevant setup information together.

7. Review fabrication before releasing the drawing

Walk the proposed part through its operation sequence. Check what must already be fitted, which straight portions remain available and how the part leaves each tool.

Separate blank preparation from finished geometry

The cut length of a blank and the finished tube's end-to-end dimensions describe different things. Define the blank through the approved fabrication method and verify the finished geometry against the drawing. The straight-end calculation above is not a developed-length calculation.

Plan cutting, deburring and cleaning as controlled handoffs. Our hydraulic tube cutting and deburring guide covers tube-end preparation in more detail. Protect prepared ends during later handling rather than assuming one cleaning step settles the whole route.

Decide when hardware and connection preparation belong

• Check whether the specified nut or sleeve can still slide into place after the bends.
• Check whether connection preparation before bending would obstruct the bending tool or damage a prepared end.
• Check whether bending first leaves enough room for the connection tool and its withdrawal.
• Record the chosen order for the part family, together with inspection and protection requirements.

There is no useful universal instruction to bend every part first or preassemble every connection first. Approve the sequence that works with the specific geometry, tooling and fitting instructions.

8. Resolve drawing conflicts before fabrication

Use the drawing review to identify a specific conflict and the evidence needed to close it. An instruction such as "allow sufficient clearance" is incomplete until the affected operation and required space are defined.

Choose a change that closes the whole conflict. Moving a bend to free the wrench is not a complete solution if it then removes the machine's grip length.

9. Validate the first tube in its installation context

Keep geometric inspection, connection preparation and installed fit as separate acceptance decisions. Passing a fixture confirms only what that fixture was designed to check.

Define what each check demonstrates

Separate connection qualification from an installation trial

ISO 19879:2021 defines test methods for metallic hydraulic connections. Its scope distinguishes test methods from the applicable component standard's test selection and performance criteria. A dimensional inspection or successful trial installation is not a substitute for those requirements. [4]

Set the necessary pressure and functional checks through the approved project procedure, with the responsible personnel and safeguards. Do not assign an arbitrary proof pressure or cycle count from a general routing guide.

Before approving repeated production, retain the accepted drawing revision and the matching material, tooling and setup records. Reassess the affected checks when any of those inputs changes.

10. Prepare the tube drawing and tooling information

A useful drawing package connects the finished shape to the method used to make and install it. Include the revised 2D/3D drawing, material and wall thickness, complete connection identification, datums and acceptance requirements. Add the available machine/tool information and any installation restrictions that cannot be understood from the part drawing alone.

How to review a hydraulic tube drawing before release

1. Confirm the inputs. Match the drawing revision to the required tube specification, operating conditions, ports and connection parts. Resolve conflicting identifiers before assessing the route.
2. Check the geometry against the tooling. Identify the bend radii, straight ends, datums and rotation references. Compare them with the actual bend and connection tools, including grip requirements.
3. Walk through fabrication. Check hardware loading, bend order, end preparation and tool withdrawal in sequence. Record any restriction that changes the order of operations.
4. Review installation and removal. Check insertion, port alignment, wrench movement and the service removal path in the intended installation. Include the required movement envelope for the application.
5. Close the acceptance record. Record the results of the specified first-part and installation checks, close drawing changes, and associate the accepted setup with the released revision.

Release the route when the connection ends, fabrication sequence and installed access have all been checked. If one remains unresolved, changing the centerline alone does not finish the design.

Frequently asked questions