Bulkhead Fittings Verse Spin Weld Fittings
A big part of our business (all manufacturing businesses really) is customer service and product advise. A question we often get asked is, “Which is better, bulkhead fittings or spin weld fittings?”
At times this can be a hard question to to answer as both product types offer pros and cons. Hopefully more pros than cons. Every time we answer this question the answer is the same: “It depends on the product application.”
What does this mean? Well, it means bulkhead fittings may be better suited to a certain application for one or other reason. Other times spin weld has clear advantages and is the best option.
To help give you a better idea we had put together a Product Application Guide for each product type. But first let’s look at each product type to get a better idea of what they.
Bulkhead Fittings
“Bulkhead fittings allows piping connections to be made to a tank. A hole is cut in the tank into which the fitting body is inserted. A locknut threads onto the body to hold it in place. The locknut puts pressure on the gasket(s) that allows it to make a liquid tight seal.”
Bulkhead Fittings Pro
- A well-designed bulkhead fitting can offer superior strength over a spin weld fitting.
- Bulkhead fittings can easily be replaced if the thread is damaged during installation or in use.
- Bulkhead fittings can be removed and replaced with a different size or type (male to female or visa versa) on provision the required installation hole is the same size.
Bulkhead Fittings Con
- A poorly designed bulkhead fitting may leak or fail you means of:
- The locking nut jumping the threads when tightened.
- If manufactured from inferior material the locking nut may split in half when tightened.
- Generally speaking, seals do not have a universal application. If the wrong seal is used for a particular application the fitting may leak. This can be costly for both your client in terms of lost product and your company in terms of a damaged brand.
- The seal may extrude itself off the body if the locking nut is over tightened.
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Male Bulkhead Fitting |
Installed Male Bulkhead Fitting |
Spin Weld Fittings
“The process of spin welding consists of generating heat by rotational friction to weld thermoplastic parts with circular joints. The spin welding machine applies force axially while rotating one part against its stationary mate. The resulting friction generates heat that melts the parts at the interface. Once rotation stops, the material cools and solidifies, forming a welded assembly.”
Spin Weld Fitting Pros
- As a single piece product, they may be more cost effective.
- As a spin weld fitting do not use a seal, if installed correctly, a spin wed fitting will not leak, regardless of the liquid being stored (chemical, diesel, water etc.).
- Once correctly installed a spin weld fitting can not come lose.
Spin Weld Fitting Cons
- The biggest draw back to spin weld fittings is stripping of threads. If the threads of an installed spin weld fitting are stripped the fitting cannot easily be replaced. The spin weld fitting needs to be cut out (usually by means of a hole saw), the hole welded up, or a larger fitting installed.
- If the spin weld fitting is not installed correctly I.e., the bond is not consistent around the entire circumstance of the fitting, the fitting will leak.
- All spin weld fittings should be tested once installed to ensure they have been welded correctly and they do not leak. This can be time consuming and costly.
- The installation process for spin weld fittings is more complicated than bulkhead fittings. Additional equipment in the form of routers ad driver need to be purchased. Additional training for staff is also required.
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TORNADO Spin Weld Fitting |
Installation driver |
Application Guidelines
| Application | Bulkhead Fittings | Spin Weld Fittings |
| DIY rainwater harvesting tanks |
X |
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| Small water storage tanks |
X |
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| Large water storage tanks |
X |
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| Chemical storage tanks |
X |
X |
| Diesel storage tank |
X |
X |
| Small caravan/trailer water tanks |
|
X |
| Small car an/trailer diesel tanks |
|
X |
| OEM products |
X |
X |
| Small complex/narrow rotomoulded parts |
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X |
Final Thoughts
Both bulkhead fittings and spin weld fittings are extremely effective products if used in the correct application.
Bulkhead fittings are extremely versatile, easy to install and easy to replace if damaged or stripped. A great option provided you know what liquid will be used in the tank (seal compatibility)
Spin weld fittings are ideal for smaller water and diesel storage tanks that are used in larger product assemblies by OEM’s. E.g., a caravan water tanks. Here the installation, of both the spin weld fitting and the outlet/inlet pipe, are controlled by the OEM (a trained staff member).
In a DIY or handyman type installation, if the thread is stripped on a spin weld fitting it almost always becomes the manufacturers responsibility/problem. In this scenario a bulkhead fitting is an easy replacement.
We hope this post has helped clear up a any questions you may have had about bulkhead and spin weld fittings.
If you have any other questions, please do not hesitate to contact us: info@roto-quip.com.
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