August 12, 2003 

'Inside Hydraulics' Newsletter

Issue 18

1. Think 'surplus' and save
2. Hydraulic fitting selection the key to leak-free hydraulic plumbing
3. More hydraulic maintenance tips
4. Free content for your web site or e-zine
5. Help us spread the word
6. Tell us what you think


Think 'surplus' and save

An often overlooked way of saving money when replacing a hydraulic component is to buy a 'surplus' new or rebuilt unit. This is particularly the case if the component you need is no longer in production or has a high price tag.

It is not uncommon for fluid power distributors and owners of hydraulic equipment to accumulate inventory of hydraulic components, which have become obsolete or surplus to their requirements. The owners of this stock are often willing to sell these components below replacement cost.

But when you consider all the different types, sizes and variations in hydraulic components and the number of manufacturers producing them, finding the exact component you require can be like "looking for a needle in a haystack".

You can dramatically increase your chances of finding a surplus component that matches your requirements by using the Internet. Hydraulic Supermarket operates an online marketplace, which is dedicated to the trading of surplus hydraulic components. This marketplace allows sellers of surplus components to submit details of components available for sale for inclusion in a database. Buyers looking for a surplus component can search this database and when a match is found, submit an offer to the seller.

To search for a surplus hydraulic component using this unique facility go to:

2.   Hydraulic fitting selection the key to leak-free hydraulic plumbing

Hydraulic plumbing leaks are often considered to be an inherent characteristic of hydraulic machines. While this may have been true 30 years ago, advances in sealing technology and the development of reliable connection systems means that today, leak-free hydraulic plumbing is readily achievable.

Reliable connections

Leak-free reliability begins at the design stage, when the type of hydraulic fitting is selected for port, tube-end and hose-end connections.

Ports - Connectors that incorporate an elastomeric seal such as UNO, BSPP and SAE 4-bolt flange offer the highest seal reliability. NPT is the least reliable type of connector for high-pressure hydraulic systems because the thread itself provides a leak path. The threads are deformed when tightened and as a result, any subsequent loosening or tightening increases the potential for leaks. In existing systems, pipe thread connections should be replaced with UNO or BSPP for leak-free reliability.

Tube and Hose Ends - ORFS tube and hose end connections feature the high seal reliability afforded by an elastomeric seal but, due to its cost, ORFS is not as widely used as compression fittings and JIC 37-degree flare.

Flared connections have gained widespread acceptance due to their simplicity and low cost. However, the metal-to-metal seal of the flare means that a permanent, leak-free joint is not always achieved, particularly in the case of tube-end connections.

Leaking flare joints can be eliminated using a purpose-built seal developed by Flaretite. The Flaretite seal is a stainless steel stamping shaped like a JIC nose, with concentric ribs that contain pre-applied Loctite sealant. When tightened, the ribs crush between the two faces of the joint, eliminating any misalignment and surface imperfections. The combination of the crush on the ribs and the Loctite ensure that a leak-free joint is achieved.

Incorrect torque

A common cause of leaks from flare joints is incorrect torque. Insufficient torque results in inadequate seat contact, while excessive torque can result in damage to the tube and fitting through cold working. The following is a simple method to ensure flare joints are correctly torqued:

  1. Finger tighten the nut until it bottoms on the seat.
  2. Using a permanent marker, draw a line lengthwise across the nut and fitting.
  3. Wrench tighten the nut until it has been rotated the number of hex flats listed in the following table:
Tube Dash SizeHex Flats
101.5 - 2.0
160.75 - 1.0
200.75 - 1.0
240.5 - 0.75


Vibration can stress plumbing, affecting connector torque and causing fatigue. Tube is more susceptible than hose. If vibration is excessive, the root cause should be addressed. Ensure all conductors are adequately supported and if necessary, replace problematic tubes with hose.

Seal damage

Having outlined the benefits of connectors that incorporate an elastomeric seal, it is important to note that their reliability is contingent on fluid temperature being maintained within acceptable limits. A single over-temperature event of sufficient magnitude can damage all the seals in a hydraulic system, resulting in numerous leaks.


A leak-free hydraulic system should be considered the norm for modern hydraulic machines - not the exception. But the proper selection, installation and maintenance of hydraulic plumbing are essential to ensure leak-free reliability.

"This book has the potential to save many organizations lots of money. It should be on the bookshelf of every engineer, supervisor, planner and technician that deals with hydraulic equipment... it's worth its weight in gold." Find out more

Alexander (Sandy) Dunn
Plant Maintenance Resource Center

3.   More hydraulic maintenance tips

For more hydraulic maintenance articles like the one above, read Brendan Casey's regular column in Machinery Lubrication. This magazine contains practical information on a wide range of maintenance issues including lubricant selection and application, contamination control, filtration and condition-monitoring of hydraulic and other rotating machinery.

If you live in the US, Canada or Europe, subscription is complimentary. To claim your subscription go to:

4. Free content for your web site or e-zine

Need some fresh, free content for your web site or e-zine? You now have permission to reprint these 'Inside Hydraulics' articles on your web site or in your e-zine, provided:

1. Each article is printed in its full form with no changes.

2. You send an e-mail to to let us know where you'll be publishing them.

3. You include the following credit at the end of each article:
About the Author: Brendan Casey has more than 16 years experience in the maintenance, repair and overhaul of mobile and industrial hydraulic equipment. For more information on reducing the operating cost and increasing the uptime of your hydraulic equipment, visit his web site:

5. Help us spread the word

If you've found our 'Inside Hydraulics' newsletter interesting and informative, then chances are you have a friend or colleague who would too. Help spread the word about 'Inside Hydraulics' by forwarding this issue to a friend or colleague. If they share your interest in hydraulics, then they will surely appreciate being told about this newsletter.

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6. Tell us what you think

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