138422537-reference-beach-russ-vacuum-pump-operation.pdf

Operation of Beach-Russ Rotary Valve Vacuum Pump used in many older vintage GE turbine systems

The Beach-Russ Rotary Valve vacuum pump is commonly used in power plants to remove entrained hydrogen in H2 Seal Oil tanks. The pump draws a vacuum, usually close to 30”, from the headspace of the Seal Oil tank. The unit is designed so that the discharge of the pump exits through an oil filled tank and then to a vent to atmosphere. The oil filled tank also serves as the lubricant supply for the bearings and rotary valves of the pump. If there is an accumulation of moisture in the tank, the level can rise up to the point where it is fed into the bearings and rotary valves. This will compromise lubrication of these parts. Another scenario is that the lighter turbine oil (Seal Oil, usually 32 ISO grade) can gradually dilute the viscosity of the oil in the tank, which is supposed to be 100 ISO grade. Most power plants deal with the accumulation of water by closing the overflow standpipe

(Green Arrow), and assigning a task to operators to open the tank drain (Blue Arrow) once per shift to drain accumulated water. The problem here is that water is allowed to accumulate and raise the level in the tank. As the water level in the bottom rises, it reaches an area of high agitation, and the result is the formation of an emulsion. This emulsion is a poor lubricant, and as a result, most of these pumps suffer premature failure. It is not unknown for some plants to schedule replacement of these units during each outage as part of their routine outage turbine maintenance program. There is no reason for these pumps to fail at such a high frequency, and if properly maintained, they can experience trouble-free long life of 30 years or more, based on experience in other applications. To avoid premature failure of this unit, the following steps must be taken:    

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Adjust the vapor purge valve (Red Arrow) so that a slight vacuum can be felt. Open standpipe overflow (Green Arrow) so that water accumulating on the bottom of the tank is pushed up and out the standpipe and into a bucket. Place a small cup under the vapor purge valve, and a placard that indicates that the valve should not be shut. Operators may see a small leak of oil from the vapor purge valve, and close it shut. Establish representative sampling for the unit. Initially, samples can be obtained by purging any water from the tank drain (Blue Arrow) and filling bottle from this point. The optimal sample point is obtained by drilling and tapping a hole for an oil sampling fitting at the spot shown by the (Red Crosshairs). Perform frequent oil analysis to determine viscosity depletion rate due to vapors being drawn into the tank from the Seal Oil Tank. Determine how long it typically takes for the viscosity to drop to an unacceptable level, and establish an oil change frequency to avoid running the pump with out-of-spec oil.

If these precautions are taken, this unit can be a very reliable vacuum pump, providing a consistent vacuum of about 30”. This will maintain seal oil purity and aid turbinegenerator commutator ring life. The Beach-Russ website is at www.beach-russ.com