Biodegradable Vane Spindle Grease (VSG) - The Green Grease
To ensure that units are available when required, operating efficiently and not incurring unnecessary maintenance costs, it is important that the wicket gate bearings and the regulating mechanisms receive sufficient lubrication. Too much can be wasteful and too little can lead to failures or at the least, wear, corrosion and/or higher forces to move the gates. The latter can result in overloading of other components. The grease also seals out dirt and water as well as prevent helps prevent corrosion of the bearings and journals. A grease lubricant has many advantages so it can be important to use one that has less environment impact. VSG is mainly canola oil which is a renewable raw material and the grease is biodegradable and has low aquatic toxicity. Plus no added heavy metals or chlorinated compounds. It works.
The first step is to refer to the turbine manufacture's original instructions and/or any subsequent notices on the lubricants and lubrication. Station experience, company procedures or input from company technical units can also be very useful in cases where the manufacturer's advice is not available or is very dated. The following material based on old information from Hydro-Québec can be used as a guide. It is expected that with modern formulations such as VSG grease that much less is required. This can be confirmed by monitoring wicket gates forces. Strain gauges and digital pressure gauges have been used. A greasing frequency of every week or two appears is common.
The pump for the lubrication system is to be operated as follows;
- Every 6 hours for turbines with a water head of <50 m (160 ft).
- Every 4 hours for heads between 50 m (160 ft) & 145 m (480 ft).
- Every 3 hours for heads >145 m (480 ft).
The total grease volume in one bearing can be estimated as follows;
Q (mm3) = 0.025 x Bearing dia. (mm) x Bearing length (mm) x 3.14, or
Q (in3) = 0.001 x Bearing dia. (in) x Bearing length (in) x 3.14
This is not replenished every cycle because it should reportedly take three cycles to replace all the grease. Each greasing cycle will replace one third of the total amount.
For a turbine having a greasing interval of every six hours, 15 wicket gates with upper and lower bearings, 25 cm (10 in) in diameter and 46 cm (18 in) in length, this would be about 2 kegs of grease. This is just the wicket gate bearings so slightly more is required for all surfaces.
Calculation - Grease volume: 15 gates x 2 bearings x 0.001 x 10 x 18 x 3.14 ÷ 3 regrease amount = 5.7 in3 X 4 intervals per day x 365 = 8,322 in3 ÷ 231 = 36 US gallons. Note that less is likely required with VSG.
A readily biodegradable grease based on canola oil. VSG is considered to be better than most other products being used now because it is not a 'will fit' from an existing product line. Instead VSG was specifically developed to meet operator requirements for hydro-electric turbines.
- VSG is READILY BIODEGRADABLE according to CEC-L-33-T-82 testing.
- VSG showed NO ACUTE TOXICITY in the Daphnia magna test.
- VSG has NO ADDED lead, zinc, barium or chlorinated paraffins.
- VSG has NO ADDED colouring agents.
- VSG has an EXTREME PRESSURE rating without the need for aggressive or unstable additives.
- VSG has EXCELLENT RESISTANCE to water washout and should stay in place longer.
- VSG has VERY GOOD rust preventing characteristics that will help protect the steel bearing journals.
- VSG is PUMPABLE down to at least -18°C without having to load the product up with oils or solvents.
- VSG is COMPATIBLE with the traditional elastomers used as seals for mineral oils.
- VSG has PERFORMANCE characteristics that are expected to be as good as or better than the greases currently being used.
- VSG can be utilized RIGHT AWAY and in most existing equipment.
- VSG has been PROVEN in-service and has approval from some of the largest utilities.
- VSG is manufactured in North American by a US owned company at an ISO registered plant by one of the leading grease companies.
- VSG is AVAILABLE in a range of containers and shipping quantities.
- VSG is normally IN STOCK and can be shipped ASAP.
Background: Automatic greasing systems can be very helpful to ensure that enough grease is getting to wicket gate bearings and when required. This is necessary to prevent wear of the bearings, corrosion of the journals and to seal out dirt and water.
However, if the system has been running trouble free for years, sometimes the knowledge required to keep it going is no longer readily available. For the personnel this could be through promotions, retirements, or changing job functions. Fortunately, there are only a few things but they do have to be done correctly. For example, do not forget to change the metal screen in the line, clean the valves properly every few years plus keep track of how they are doing. Most systems have counters to help ensure that the systems are working but someone has to record and track them. Monitoring grease consumption through stores withdrawals can also help.
- Use a suitable grease with good pumpability, good resistance to oil separation and with no solids that can separate out. It should be an extreme pressure rated grease.
- Replace dinged, crimped or damaged lines.
- Do not use too high an air pressure for the grease pump. More is not better. If a 50:1 pump use as a max the rupture disk rating (or any other rating if lower) divided by 60 or as recommended by the pump supplier. Air pressure should typically be about 50 psi.
- Clean the grease pump air filter, water trap and regulator as required. Verify.
- Change or inspect the grease screens annually.
- If cleaning only do this a maximum number of times, possibly five. For example, discard every year divisible by 5.
- If changing grease types or brands, determine the grease compatibility including tests on the key characteristics for the mixtures.
- Clean the distributer valves at least every ten years. It might have to more often with a soap based grease. Return each piston to the same segment in the same orientation.
- Keep track of grease consumption to identify problems and do not let a pump operate dry. Too little is not good for the bearings or the equipment.
- Track counts for all systems to ensure that grease is getting to the application points. Where possible check that some grease can be seen coming out and that it is clean. It should be a bit darker but should not be have metal pieces, have rust or be blackened.
Correct the root cause of any rupture disks replacements. Do not just put in a higher rated disk because this can lead to more oil separation or other problems. It can also be helpful to talk to your grease and/or equipment supplier because new offerings might be available. For the greasing systems this could include better grease line performance indicators and alarms.
Many stations use an automatic grease lubrication system to ensure that the wicket gate bearings and the regulating mechanisms receive sufficient lubrication. It is important that the right amounts at the right times are delivered because too much can be wasteful and too little can lead to failures or at the least, wear, corrosion and/or higher forces to move the gates. Too little can also mean that what grease is being provided stays in the supply lines too long. The grease also seals out dirt and water as well as help prevent corrosion of the bearings and journals so a slight excess is considered to less likely to cause subsequent problems.
Wicket gates are generally lubricated 1-4 times a day and the other mechanisms twice a week. Take care reducing the frequency without proper feedback or monitoring such as the operating system pressures or linkage/arm forces. This is because a plugged grease system can be labor intensive to clean and worn bearings and/or journals (shafts) expensive to replace or repair.
Grease Line Plugging
Central greasing systems are much like oil systems with a grease reservoir as a container, typically a keg or drum, a pump, a grease metering system (valve blocks) and a distribution system. There will also be a relief valve. Filters are not used but there might be metal mesh screens in the line downstream of the pump.
The systems at hydroelectric stations are different than typical industrial systems because the lines can be very long and at the some end points at the bearings the greases are subjected to a water stream. Also, because they are indoors the ambient conditions are moderate with expected operating temperatures of 10°C (50°F) to 30°C (86°F). This is important because low temperatures can cause grease mobility issues and higher temperatures can speed up oil separation and/or oil degradation.
Once any issues with the grease pump, relief valves passing, air in lines, follower plate stuck or missing and lines being damaged are eliminated, high pressures because of grease line plugging can be the result of the grease being too difficult to move. The root cause can be one or more of the following;
Grease too stiff in first place: Generally use a Grade 0 or 1 but this is only a rough guide to true mobility. In general a higher NLGI (National Lubricating Grease Institute) Grade is better for the bearings and water washout resistance.
Grease too hard to move: Must be sufficiently mobile. Check USX mobility and/or Lincoln pumpability. Too high a base oil viscosity or a poor quality base oil with a low VI (viscosity index) can contribute to excessive pressures. These can then cause more oil separation.
Oil Separation: Some greases, especially under pressure, release the oil. This then leaves the thickener (sometimes a soap) behind that plugs the lines.
Solids Separation: The use of solids like moly, graphite and PTFE can be a problem if they separate out over time or get caught on metal screens. Generally avoided. If unstable additives are used these can also drop out and contribute to line plugging.
Constrictions: Over time deposits can form in the lines or valves. These can be from the grease, dirt and/or corrosion. Lines also get dinged so a periodic replacement program could help and some stations use nylon rather than copper tubing.
Another factor, especially when switching greases, is compatibility. Because different grease thickeners might have been used as well as various oils and additives the mixed greases can sometimes react. While less of a problem at the low temperatures of this application, the consequences can be mixtures that can be stiffer or softer. If stiffer they can be harder to pump and even if softer there can be concern about increased oil separation or water washout. Verify compatibility before use and in some cases an intermediate grease compatible with both can be used for a few greasing cycles.
In addition, excessive grease pressures can be the result of plugged bearing clearances. The cause can be silt or hardened grease because of insufficient greasing.
While the application appears simple a few utilities have detailed specifications for wicket gates. Basic ones just copy some parameters for a grease that worked in the past while others have performance provisions to avoid specific problems. Many such problems were related to grease mobility that can contribute to line plugging. Unfortunately, few of the existing wicket gate grease specifications appear have updated recently to take into account new requirements and new products. This is not thought to be because there are fewer problems but rather inappropriate cost accounting and diminished tech support available to the stations.