ASK ERNIE What is the difference in mechanical seals and pump packing? Pros and cons of each?
Prior to mechanical seals, every pump had a mechanical seal of some style. Early centrifugal and positive displacement pumps had a rope style packing with a grease fitting of one of may types to keep the packing lubed and resilient.Today, we have a pump packing of newer and more resilient composites that require no lubrication. Darley Pump Company uses both the old ‘Plastalic’ injection packing that assumed the role of the common rope packing with a much easier means of adjustment. As the packing became washed out and ‘worn,’ it would no longer stop leaking or would leak at a much too high rate.This situation led to ‘over-adjusting’ the packing in an attempt to achieve a drip free condition while on the apparatus floor.The over-tightening led to high heat and scoring
of the shaft. Once the shaft was substantially damaged by scoring, no amount of new packing would cure the problem of leakage.The packing style pump had the ability of being ‘re-packed’ by removing the old packing and installing new. It was not fun, but could restore the packing to its original leak rate while pumping if the shaft had not been scored and could be accomplished without major disassembly of the pump. Mechanical seals in firefighting pumps are likened to the mechanical seal in the modern day centrifugal water pump that circulates coolant through the motor. Coolant water pumps can go without changing for the life of the automobile if the coolant is maintained in proper condition.The mechanical seal in the firefighting pump can also last the life of the pump if clean water is flowed through the pump and the seal is not allowed to EVER overheat due to loss of water.
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However, every time the water tank goes dry with no water available to the seal surfaces, those surfaces — ceramic and hard carbon — become extremely hot. When cool/cold water does make contact with these overheated seal surfaces, the result is usually a cracked component of the seal surfaces. The result: an external leak and a negative pressure leak during drafting situations. Replacement of the mechanical seals is usually a very labor intensive task. Some pumps utilize a single mechanical seal, some use double shaft-end seals.The preferred seal today is the mechanical seal due to its total leak free ability and long service life. Packing style pumps are still available, but are fewer each year. What is the correct drip rate for pump packing Waterous and Hale?
Old Uncle Ernie is not falling for this one. Get out your manuals and check the drip rate for the pump you are asking about. A mechanical seal pump has a zero drip rate allowed. A packing style pump has a drip rate as designed into a particular pump by the engineers to keep the pump shaft and packing cool while pumping water. A drip rate is one that occurs only under hydrant situations where a single stuffing box is utilized — like Hale — and on a double stuffing box pump — like Waterous. If the pump is a single stage, the packings only leak while at hydrant. If the Wa-
terous style pump with dual stuffing boxes on a two stage pump is used, the pressure/series mode will leak only at the compound side of the pump. How often should I perform a drift test on my aerial hydraulics?
The aerial drift test is an annual test performed at 60 degrees elevation and full extension.The drift test is for a period of one hour and may not drift more than the manufacturer’s specified amount. Refer to NFPA 1911; Standard for the Inspection, Maintenance, Testing, and Retirement of In-Service Automotive Fire Apparatus, 2007 Edition. Section 19.8.4.16.2; 19.8.5.8.2; 19.8.6.28.2 and others, depending on the type of aerial apparatus. Please note that all aerials must operate with no Class 3 fluid leaks and should be evaluated for immediate hose replacement or component repair if it has a Class 2 leak.
What interlocks does my truck have if it is after 2010 and what interlocks does it have if it is older?
Today’s apparatus have many more interlocks than in the past. Electronic motors and multiplex’s electrical systems allow for more interlocks for the safety of the operator. On a pumper, things like: if you have not achieved parking brake set confirmation, pump engagement confirmation; idle confirmation, the pump panel throttle
will not activate. In an older mechanical motor, if an error was made — usually through the stress of the moment — and the transmission was left in “D” gear and then a move was made to shift the lever from “Road Mode” to “Pump Mode,” no movement of the pump gearing would occur because of the torque on the slider gear in the Road Mode.The result, when the operator got to the pump panel and began the unrestricted throttle up on the mechanical engine, the torque in first gear converter would finally overcome the parking brake and the pumper would leave the scene. Many occurrances of this type happened in years gone by.Thank goodness for these interlocks today. If you are operating an aerial device, interlocks abound. If the stabilizers
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