May 18, 2004 

'Inside Hydraulics' Newsletter

1. The emergence of the 37-degree fitting in no-leak hydraulics
2. Hydraulic oil, detergent additives and manufacturers' recommendations
3. How to define and achieve hydraulic fluid cleanliness
4. Content for your web site or e-zine
5. Help us spread the word
6. Tell us what you think


The emergence of the 37-degree fitting in no-leak hydraulics

The 37-degree flared fitting is the world's most commonly used hydraulic connection. This popularity is due to its ease of fabrication, wide size range, adaptability to metric tubing and worldwide availability. For over fifty years, it has been the fitting of choice for nearly all hydraulic system manufacturers. As technology has improved and standard system pressures have steadily increased, the flared fitting has become prone to leaks and drips, which results in dirty, sludge-covered systems that give hydraulics a bad name. The cost to industry and the environment is only now being fully considered.

Alternative fittings are gaining acceptance, most notably the 'O-Ring Face Seal' (ORFS). The ORFS fitting has significantly improved the integrity of hydraulic connections, but at a cost. It is larger in size, offers fewer adapter options, is more difficult to install (alignment must be perfect or O-ring extrusion occurs), has limited worldwide availability, is twice the price of a flared connection, and the O-ring is susceptible to environmental failure.

In June 2000, Norm Mathers, President of Flaretite Pty. Ltd. released a new sealing device for use with flared tube and fittings. The technology of this seal has propelled the old, flared connection into the new "No-Leak" world demanded by modern hydraulic systems.

The Flaretite Seal is a stainless steel stamping, designed with multiple, concentric rings. The entire seal is impregnated with a baked-on Loctite coating. When inserted into a flared fitting, the concentric rings form multiple seals down the face of the flare and the Loctite coating fills minor imperfections. The sealing rings prevent environmental debris and aggressive cleaning solvents from attacking the sealing face and also protect the face from fretting, galling and over-tightening. And unlike the ORFS fittings, the Flaretite Seal will not fail during a fire. This prevents atomized hydraulic oil from fueling combustion.

Flaretite seal in cross-section.

Flaretite Seals are easy to install. They snap onto the male end of the flare and the fitting is tightened in the usual way. The result is a permanent, zero-leak connection which exceeds the performance of today's ORFS fittings, at significantly less cost.

Flaretite Seals are available through Eaton-Aeroquip and Eaton-Weatherhead distributors, and many other quality-conscious hydraulic distributors. Eaton has thoroughly tested the Flaretite Seal with extensive 1,000,000+ square wave cycle testing. In all cases, the seal passed the stringent test requirements with no failures. Flared connections fitted with Flaretite Seals are today's answer to low cost, high integrity, "Zero-Leak" fittings.

For more information visit or contact Vito Accetta, Operations Manager at Flaretite, Inc. located in Fenton, Michigan, USA.

2.   Hydraulic oil, detergent additives and manufacturers' recommendations

I recently came across the following story posted on a message board by a heavy equipment mechanic:

 " I have a customer who recently bought a new service and operator's manual for his old Komatsu PC150 excavator… He went to the lubrication guide for the hydraulic system and chose what the chart said was a 10W-40 engine oil and got what Texaco showed as being Komatsu's recommendation. Here is where the problems begin... First you never want to use a detergent oil in a hydraulic system - it can cause anything from foaming in the oil which will cause cavitation in the pump and result in premature pump failure, to it picking up waste/contaminants in the oil and depositing it as sludge throughout the system. But according to Texaco EVERY multi-grade oil available in the US is gonna be a detergent oil... Second, and I actually called Komatsu America on this, they DO NOT recommend a detergent oil in the hydraulic system...What is supposed to be in the hydraulic system is either a 10W or a 30W non detergent oil... This tells me that there are a lot of people out there that are blissfully going by the book and slowly killing their machine's hydraulics. Hopefully at least some of them have asked before they wasted a lot of money and filled their system with the wrong oil. My customer is a long-time equipment owner, so didn't ask me before he changed his oil... the book has to be right, right?... Now he's stuck with a 50 gallon system that he can only change 30 gallons of at a time so it's going to cost him big to fill and flush enough times to get all of the detergent oil out of the system…"

When the OEM doesn't say what they mean, it can certainly make it difficult to follow their lube recommendations. But is a detergent oil, such as a multi-grade diesel engine oil, really detrimental to a modern hydraulic system?

Detergent additives

DIN 51524; HLPD fluids are a class of hydraulic fluids which contain detersive and dispersive additives. The use of these fluids is approved by most major hydraulic component manufacturers and can be advantageous in many applications, including mobile, to prevent build-up of sludge and varnish deposits, which can lead to valve stiction and other reliability problems. The main caution with these fluids is that they have excellent water emulsifying ability, which means that if present, water is not separated out of the fluid. Emulsified water reduces lubricity and filterability, can cause corrosion and cavitation and reduces the life of the oil. These problems can be avoided by maintaining water content below 0.1% - which is not a low water content target for any high-performance hydraulic system. A hydraulic fluid that has the ability to emulsify small amounts of water can be beneficial in mobile applications.

Modern lube chemistry means that detersive and air-separation/anti-foaming properties aren't necessarily mutually exclusive. At least one major, mobile equipment manufacturer specifies heavy-duty diesel engine oil to API classifications CD, CF-4, CG-4 or CH-4 as an acceptable alternative to a single-grade, anti-wear, hydraulic oil in their equipment.

Viscosity index improvers

This is not to say that mutli-grade engine oils are suitable for use in all hydraulic systems. Multi-grade engine oil, automatic transmission fluid and anti-wear, high VI (AWH) hydraulic fluid are commonly used in hydraulic systems that experience a wide operating temperature range. These fluids have a higher Viscosity Index (VI) than standard anti-wear hydraulic fluids due to the addition of VI improvers. The higher the VI a fluid has the smaller the variation in viscosity as temperature changes.

In simple terms, this means that if you are running a 10W-40 engine oil in your excavator hydraulics, you can operate the hydraulics with a higher fluid temperature before viscosity falls below optimum, than you could if you were running a single-grade, anti-wear, hydraulic fluid.

When selecting a high VI fluid, it is wise to increase the hydraulic component manufacturer's minimum permissible viscosity value by 30% to compensate for possible loss of viscosity as a result of VI improver sheardown. VI improvers can also have a negative effect on the air-separation properties of the fluid and for this reason some hydraulic component manufacturers recommend that high VI fluids only be used when operating conditions demand.


As far as fluid recommendations go, for commercial reasons relating to warranty etc, it is always advisable to follow the machine manufacturer's recommendation. But on the other hand, if you were to realize retrospectively that the hydraulic system of your excavator or dozer had been inadvertently charged with a multi-grade, diesel-engine oil, it's not necessary to press the panic button either. Discussing the application with a technical specialist from the oil manufacturer, in conjunction with the OEM, would however be advisable.

If you think this failure looks expensive - you're right! To find out what caused this failure and how it could have been avoided, read Preventing Hydraulic Failures. Find out more

3.   How to define and achieve hydraulic fluid cleanliness

For some practical advice on how to define and achieve hydraulic fluid cleanliness, read Brendan Casey's article in the March-April Issue of Machinery Lubrication magazine, available here. To receive a complimentary subscription to this informative magazine (US and Canada only) go to:

4. Content for your web site or e-zine

Need some fresh 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 advise us where you'll be publishing them.

3. You include the following acknowledgement 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:

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