Sep. 25, 2024
In a rear-wheel drive vehicle, the transmission’s power must be transmitted from the front of the vehicle to the rear wheels. This is done using a driveshaft – a long metal shaft that attaches to the end of the transmission and turns with the rotational speed of the transmission and the engine. However, the driveshaft cannot connect directly with the rear wheels. A differential is used to transform the rotational power of the driveshaft into movement at the wheels. To connect the differential and the driveshaft, a pinion shaft is used.
Depending on the make and model of vehicle in question, there will be one or more pinion seals. One will be located at the inner edge of the pinion shaft, and another (the pinion shaft oil seal) will be located near the end where the pinion shaft attaches to the drive shaft. The point of the seal is to prevent oil from leaking out of the pinion shaft.
All seals are subject to wear and tear, as well as degradation from heat. Eventually, they will fail. Your pinion shaft oil seal is no different. There’s no estimate on how long one should last, though, as there are many different mitigating factors. The seal is in use anytime you’re driving, and your driving habits and the conditions in your area will have significant effects on the longevity of the seal. For instance, if you regularly go off-road with your vehicle, you’ll but a lot more wear and tear on the seal than someone who sticks to the pavement.
The most important tip to remember about your pinion shaft oil seal is that it should be inspected for leaks at every service (your regular oil change, for instance). Once a leak is spotted, the seal should be replaced, as it will only become worse over time. Here are a few common symptoms of a failing pinion shaft oil seal to watch for:
Wetness at the end of the pinion shaft/driveshaft
Low differential fluid
Whining or grinding from the differential while driving, particularly around curves (indicates low fluid)
If you suspect there’s a problem with your pinion shaft oil seal, a certified mechanic can help inspect the system and replace the pinion shaft oil seal if necessary.
Have you ever received the dreaded 2 a.m. call from plant staff saying that things are at a standstill – production is down?
You arrive at the plant, walk through the parking lot, coffee in hand, and head to the locker room. When you come out on to the plant floor, there are several people staring at you with a look of panic on their faces as steam or process chemical sprays from a pipe flange.
Prognosis……gasket blowout.
You think to yourself “didn’t we just replace that gasket?”, or perhaps “we should have replaced it during the last shutdown but chose not to because of time constraints or cost cutting.”
If this scenario is new to you, you are lucky and you can go back to sleep… the 2 a.m. call was a wrong number. If it’s not new to you, this means you are most likely a Plant Supervisor, Maintenance Manager or Plant Personnel in some capacity.
Roll up your sleeves, grab your torque wrench and let’s get to work!
If I had a nickel for every time someone asked me, “How long will my gasket last?” I would be a rich man. As you can probably guess, “How long will my gasket last?” is a loaded question to which the practical, factual, and political answer is… an Application Engineer’s nightmare!
A gasket may last 5 years, or it could last 20 years. I cannot give you an exact date or lifespan of a gasket; however I can give you some insight into factors that will give your gasket the best chance at a long and prosperous life between the flanges.
Gasket Selection
Choosing the right gasket will save you a lot of grief. It’s important to speak with an Applications Engineer to help determine the proper gasket for your application. Factors such as chemical compatibility or elevated temperature can severely affect elastomer-based gaskets and cause them to become brittle. When gaskets become brittle they lose their ability to expand and contract with cyclic conditions. Sometimes they can start to leak slightly and the natural urge is to just “snug” or re-tighten the bolts with your wrench… DO NOT DO THIS.
Remember the gasket is brittle and now re-tightening this gasket may cause it to crack or break, leading to a blowout which can cause serious issues.
2. Gasket Quality
As a gasket manufacturer, I can tell you that cost matters. For instance a $2.00 compressed gasket may last 1 – 5 years, but a more expensive gasket, such as a $25.00 gasket could last 20 years. You don’t necessarily need to buy the most expensive gasket on the market; however, saving 50¢ on a lower-priced gasket should not be high on your priority list forsaking reliability and safety. In the end, you get what you pay for (within reason).
3. Installation
Installation is the most important factor to gasket longevity. Failing to install a gasket correctly is starting off on the wrong foot and indeed setting yourself up for a premature failure. Consider the following before gasket installation:
Do you have an installation procedure?
Do you use a torque wrench?
Do you know what torque values must be used?
If you answered ‘No’ to any of the above questions, I highly suggest you reach out to your gasket manufacturer for recommended installation procedures and appropriate torque values. Better yet – get your hands on a copy of ASME PCC-1 and read it if you’re serious about extending the life of your gaskets.
There is no real way to predict the future and determine when gasket failure will occur. To ensure you get the best performance out of your gaskets, following these suggestions will ensure that your gaskets don’t prematurely end up in the trash bin. And maybe you won’t get any more of those dreaded 2 a.m. phone calls.
Until next time, stay safe and keep the fluid between the pipes!
For more information about how Gallagher Fluid Seals can help you solve gasket challenges or how we can provide custom solutions to you, contact our engineering department at 800-822-4063
Original article was writted by Chett Norton, C.E.T. and can be found on the Triangle Fluid Controls website.
Seal life is very difficult to determine on equipment in the field because operating conditions are unknown, and they vary considerably. It’s hard to define a “typical” application. Furthermore, the applications are usually not ideal (defined as clean lab type environments, fully lubricated, low speed, ambient temps, no pressure, no misalignment or runout, no exposure to chemicals or solids, everything is sized correctly, etc), and the reality is that these factors change seal life considerably.
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hemicat wrote:....Usually where the seal lip rides on the crank. You will find a groove worn on the end of the crank. When this happens you have several options. First option if you are lucky they offer a wear sleeve. This will fit over the end of the crank and give you a quick fresh surface and you can continue on. If not then you are faced with either having your crank turned or looking for a replacement...
The front seal on an ACVW rides on the flywheel, not the crank. A "speedi-sleeve" fix might work, if one were available - but I've never heard of one for the VW flywheel.
Sagaboy's flywheel shows some pretty serious pitting, personally I'd replace it if I was hoping to be totally leak-free. If that's not in the cards, I'd polish it with emery cloth and use an orange hi-silicon seal. Preferably a double-lip, but if only a single-lip could be found I'd put it in at a different depth than the old one (i.e., if the old one was only flush with the case surface put the new one in until it bottoms in the bore - or vise-versa) and cross my fingers.
The oil on the clutch disk got there by bypassing the O-ring seal inside the flywheel snout. That must be replaced, a new flywheel seal alone won't fix that problem.
The front seal on an ACVW rides on the flywheel, not the crank. A "speedi-sleeve" fix might work, if one were available - but I've never heard of one for the VW flywheel.Sagaboy's flywheel shows some pretty serious pitting, personally I'd replace it if I was hoping to be totally leak-free. If that's not in the cards, I'd polish it with emery cloth and use an orange hi-silicon seal. Preferably a double-lip, but if only a single-lip could be found I'd put it in at a different depth than the old one (i.e., if the old one was only flush with the case surface put the new one in until it bottoms in the bore - or vise-versa) and cross my fingers.The oil on the clutch disk got there by bypassing the O-ring seal inside the flywheel snout. That must be replaced, a new flywheel seal alone won't fix that problem.
Five performance factors affect the life of a mechanical seal and guide the determination of an optimum replacement cycle for that seal. They also lead to improved seal life and mean time between repair (MTBR), thereby reducing the Life Cycle Cost (LCC) of the pump population.
Last month we reviewed the first two of these factors. Here are the other three.
Seal Application Limits
The third factor is published mechanical seal application limits, typically defined by pressure, speed and temperature, are prone to misinterpretation.
Most seal manufacturers say that operation of the seal at one of these limits will result in a minimum life span of two years; three years with some seal types such as those specified in Standard API 682. The published limits, while reliable for steady state operation, may be overstated or unreliable for cyclic operation. An exception may be API 682 seals, which specifically address that shortcoming by including a series of cyclic tests to qualify a specific seal type for a range of services.
Generally, no fixed rules exist on how much particular transient-pressure, speed, temperature, gas or solid entrapment, or vibration a seal can tolerate. Expert advice is needed in this area.
Seal Face Deflection
The amount a seal face deflects during a transient depends on several factors, including the magnitude and rate of the transient, and the robustness or strength of the seal face. The bottom line is that seal face deflections occur as operating conditions change and may either improve or starve lubrication of the seal faces. A reliable seal is one having a low degree of sensitivity to the expected or unexpected transients. The sensitivity of a seal can be defined by its ability to maintain more or less parallel seal faces during all possible transients.
Sensitivity can also be controlled by properly selecting the materials and the environmental control system. For example, seals with hard/hard face combinations, such as tungsten carbide (WC) and silicon carbide (SiC), which are preferred for dirty fluids or in some cases for high pressures, are very vulnerable to complete or partial loss of the fluid film. Any type of damage to these materials, when run against each other, is typically unrecoverable and only gets worse as time progresses.
New face materials and treatment technologies, such as diamond coatings, promise significant improvement in this area. On the other hand, hard/soft combinations with carbon-graphite as the wearing material offer the distinctive advantage that they can carry much higher loads, sustain longer periods of inadequate lubrication and, most importantly, more readily recover after damage to the carbon-graphite face.
Silicon carbide against a hard carbon-graphite is generally accepted to have one of the highest load capability limits of the readily available materials, best tolerates dry running and, therefore, should be the preferred material combination for many applications.
Limiting Application Parameters
Without question, an application becomes more difficult and risky when using a larger shaft diameter, faster speed, and higher temperature, pressure and solids content. It is imperative that the robustness of the faces and their ability to dissipate heat efficiently are optimized accordingly.
In many tough applications, it may be wise to consider custom engineered mechanical seals that are designed specifically to deal with unusual events or predefined operating modes of the equipment. Different face designs and lubrication technologies can be selected to increase the life of the faces.
Seal life well in excess of three years is possible for the large majority of applications. The seal face shown in Figure 1 is an example of a robust design that is used in high pressure or speed applications with the ability to handle severe transients and periods of inadequate lubrication. The carbon-graphite face is shrunk-fit into a metal housing and reinforced at the inside diameter with a hardened steel ring. The API 682 and Hydraulic Institute publication Mechanical Seals for Pumps: Application Guidelines offers good rules for specifying an engineered seal.
Leakage requirements
The fourth factor is all face seals must leak a minute amount to sustain an adequate lubricating film during all operating modes.
Because seals operate in these favorable lubrication regimes, energy consumption is minimized, which makes seal operation more economical. The amount of leakage is typically a few milliliters per day or less and not visible. This may be significantly higher for special applications involving high pressures, speeds or large shaft diameters. Consult your seal vendor for the calculation of expected leak rates.
Mechanical seals meet today's emission limitations in the vast majority of applications. Predicting the leakage and friction behavior for any given application is possible with a good degree of accuracy, which helps set operator guidelines for normal, questionable, and failure behaviors of the seal.
The leak rate increases or decreases when conditions such as pressure, temperature, or speed are changed. This means the leak rate varies depending on how the pump is operated and how responsive the seal faces are to any transient operating conditions. The key to a low and consistent leakage pattern is to maintain face flatness. The Key Performance Indicators (KPIs) of the seal may differ depending on the face technology and materials used.
Any given application usually has several solutions that vary widely in cost and benefits. Seal vendors often promote unique features to enhance or optimize the lubrication of the faces. Some OEMs promote hard/hard combinations for high pressure applications, whereas others uphold the hard/soft approach. Each differs in their ability to cope with unusual events, and the best choice is not always evident.
Seal Environment
Finally, the seal is only as reliable as the environment in which it operates.
The operating environment can be manipulated or controlled by selecting and applying a suitable system from a wide choice of methods - and that is almost as important as the seal itself. Most seals need a flushing system to evacuate the heat developed by the seal. If this system malfunctions it may cause problems. "A cool seal is a happy seal" remains true for the majority of applications.
Some fluids may change state as pressure or temperature changes. In the seal chamber the faces are exposed to the suction or discharge conditions of the pump, while at the seal face gap the fluid pressure reduces and its temperature increases. At the exit of the seal faces, the pressure and temperature are close to ambient. The point here is that as pressure and temperature change, the fluid properties may be significantly altered and possibly cause trouble for the seal if not addressed when selecting the seal and control system.
Environmental control systems can be applied to prevent or minimize the negative affect of certain transients, remove the frictional heat of the faces, reduce the presence of solids in the flush flow, improve conditions to prevent vaporization or freezing of the fluid. Most importantly, they minimize the consequences of a failure to the surrounding environment.
A wide choice of flush plans is included in ANSI, API and ISO standards. The variety of seal types and materials, combined with a wide array of flush plans, can make seal selection quite challenging. Helpful hints and tools, such as the FSA Seal Life Cycle Cost Estimator, can be found on www.fluidsealing.com. This tool can compare a wide variety of seal types and systems to aid with effective seal system selection.
Selecting the "Most Effective Sealing Technology" requires a sound understanding of what drives seal performance behavior . . . not only under normal operating conditions, but more importantly, under abnormal conditions.
Next Month: When should I use braided PTFE packing and in what form?
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