Spatial Allowance for Fittings in Fluid and Gas Systems

Spacial allowance for fittings in fluid and gas systems is important to remember during the design phase.We frequently get calls from our customers who find themselves in the late stages of development and have an unexpected complication with their design which requires our help. They are assembling their system except the fittings they planned to use do not have the adequate space needed. This means that a design change is required late in the game, which could mean a custom fitting or having to completely reroute the hoses or tubing. This article should point out a few things to consider while you are developing your design plan so that you can avoid these types of situations.

Considerations for fitting connections during system design

Hydraulic fittings are used in many different industries, and most companies do not have engineers who specialize in fluid system layouts.  Meaning, a product line engineer may be expected to plumb a hydraulic system that is only partially designed. Not many people are expected to be specialists in line routing and what are the best fittings to use and where, so they may find they have plumbed themselves into a corner.  

Consider the assembly space needed for tightening fitting connections with a wrench.While fittings are not always viewed as top priority, keep them in the back of your mind during the design process. It’s not necessary to choose a style of fitting at the beginning of the process but think through what you need the fitting to do and how you’ll need to access it. Wrench clearance is extremely important with fittings, so you will want to consider assembly as well. For example, if you choose to use an adjustable elbow fitting, your assembly process will be different than if you use a swivel elbow.


Fittings by nature are components in a larger system. This means that they will often be surrounded by a variety of non-moveable obstructions. When you are designing your system, consider how accessible they are. It’s important that fittings and hoses are in a position that will allow for the required regular maintenance without needing to completely disassemble the entire system.


Allowing space for assembly 

A specific example to consider may be the tightening/assembly difference between O-Ring Face Seal (ORFS) and 37-degree flare style fittings. One of the advantages of an ORFS fitting is that you only need room for a 20 degree turn of the tube nut or hose swivel nut. A 37-degree JIC fitting however, needs up to a 120 degree rotation angle. For more information, check out the post Turn vs. Torque? How Making the Right Choice Keeps Your Hydraulic Fitting Connections Leak-Free.

Zero clearance fittings, such as O-ring Face Seal (ORFS) allow for the tubes to be assembled into place on a system without the concern for tube insertion depth (see Figure 1). Tube insertion can create an assembly order of operations that may cause unintended headaches. A zero-clearance fitting avoids that headache completely. In some applications this design feature is quite helpful with making the assembly process smoother. For more information on the different tube and hose end sealing types, it may be helpful to review our post A Closer Look at O-ring Face Seal, 37-degree and 24-degree Flareless Fittings

ORFS fittings offer zero clearance tube assembly whereas 37-degree fittings require tube insertion for assembly.













Figure 1. ORFS seat vs. 37-degree flare seat


Order of operations for assembly

When designing a fluid system, it is critical to think of the order of operations for assembly. The assembly of different connections can get quite complicated, so you need to be actively thinking about what standard fittings are available for the fitting style you have chosen. Therefore placement of fittings in a system whether it be directly mounted to one component or an in-line fitting may impact your ability to connect the system together. For more information on tube routing, and for more real-world examples, refer to Tube Routing Tips for Hydraulic, Pneumatic and Lubrication Systems.  

Here are the things we recommend you consider during your fluid system design process:

  • Have you considered wrench assembly clearance? A 37 degree flare fitting will need space to allow for up to a 120 degree turn.  Is there enough room to get a wrench or a socket in?
  • What is the working pressure of my system? This will help you determine which sealing type you need. Determining the seal type will give you an idea of the fitting dimensions you need to accommodate.
  • Have you considered thread type? Avoid pipe threaded ports where possible, due to the inability to orient, straight thread O-ring boss ports are preferred.
  • What is the order of operation for assembly? As components are added into your system, could you route a fitting in a different direction to allow for better access?
  • What is space claim for the fitting going to be? Is your design rigid, will you have the ability to move components around? Are your fittings going to run into other fittings or components?
  • Is the system you’re creating going to require a custom or jump size fittings? Could that be avoided with a simple design change, such as a tube end reducer? Though customs can be made, replacement parts may be more difficult to find or could extend production lead times.
  • Have you thought about repair work? Does your assembly make it easy to repair or maintain your system when needed? Will you need to disassemble the whole system to get access to a filter that needs replaced?

In summary, when designing your system it’s important to keep fitting connections in mind by creating a checklist of what to take into consideration. As we discussed, the following items may be great to start with: assembly clearance, working pressure, thread type, assembly order of operations, what standard fittings could be used, and any repair work that may be needed in the future. Fitting considerations such as these are rarely on a designer's radar. Reviewing this list before designing your systems will avoid complications down the line, making both production and maintenance easier which will save you and others many headaches. 

Refer to our Tube Fittings Division Frequently Asked Questions page,, for a wealth of information and resources. 

If you have any questions or comments, please post them, and we will respond if warranted. To talk to our techConnect engineer team directly, they can be reached at Parker Tube Fittings Division, 614.279.7070. See Parker Tube Fittings Division's full line of tube fittings and hose adapters

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Emily Alexander, senior design engineer at Parker Tube Fittings Division

Contributed by Emily Alexander, senior design engineer at Parker Tube Fittings Division and Ted Amling, senior project engineer at Parker Tube Fittings Division





Ted Amling, senior project engineer, Parker Tube Fittings Division







Additional related content about hydraulic tube, hose and port fitting connections:

Assembly Instructions for Ensuring Leak-Free O-ring Face Seal Fittings

Sizing Tube to Maximize Hydraulic System Efficiency

A Dollars and Sense Approach to Preventing Hydraulic Oil Leaks

6 Tips to Improve Your Plumbing and Assembly of Hydraulic Tube, Hose and Port Connections

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