Transcript
Operation of Beach-Russ Rotary Valve Vacuum Pump used in many older vintage GE turbine systems
The The Beach-Ru -Russ Rot Rotary Valv Valve e vacuum pump is commonly used in power plan lants to remove entrained hydrogen hydrogen in H2 Se Seal Oi Oil tanks. tanks. The pump draws draws a vacuum, usual usually close close to 30”, 30”, from the head headspa space of the Seal Seal Oil Oi l tank. tank. The unit unit is is designe signed so tha thatt the discharge discharge of the pump exi exits ts through an oil oil filled tank and and then to a vent to atmosphere. The The oil filled tank also lso serves as the lub lubrica icant supply for for the bearing ings and rotary valve lves of the pump. I f there is is an an accum accumulation ulation of moisture oisture in thetank, tank, the level can rise rise up to the the point where it is is fed into thebearings rings and rota rotary valves. This his wil will compromise lubrication of these parts. parts. A nothe nother scenario rio is is tha that the the lighte ghter turbine oil oil (Seal (Seal Oil Oil, usua usuallly 32 I SO grade) can gradua gradually di dillutetheviscos viscosiity of theoil oil in the the tank, tank, which which is supposed to be 100 100 ISO ISO grade. Most power plan plants ts deal with wi th the the accum accumulation ulation of water by closi closing ng the the overfl overflow standpipe standpipe
(Green Arrow), and assigning a task to operators to open thetank drain (Blue Arrow) once per shift to drain accumulated water. The problem here is that water is allowed to accumulateand raise thelevel in the tank. As the water level in thebottomrises, it reaches an area of high agitation, and the result is theformation 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 someplants to schedule replacement of theseunits 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:
Adjust the vapor purge valve (Red Arrow) so that a slight vacuumcan be felt. Open standpipe overflow (Green Arrow) so that water accumulating on the bottomof 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 beobtained by purging any water from thetank 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 vacuumpump, 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
