What is the original reason for departments to have two stage pumps?
OK, Uncle Ernie is old, but not that old. However, there are several reasons for a two-stage pump versus single stage. Back in the early days, the gasoline engines were of low horsepower and torque. To get a decent stream at high pressure, the two-stage pump was needed. Consider that in pressure mode (series) the pump can be considered as one-half rated pump capacity at twice the pressure. If the water stream needs to reach greater heights, a smaller bore nozzle is selected and switched to pressure mode. Working wildland areas with substantial mountainous rises in elevation; you needed the greater pressure to get any decent flow from the nozzle at that elevation. Thus, volume mode (parallel) gave you twice volume and one-half pressure. If you were called to a high rise building and needed to get fire streams to upper levels or pump a high rise stand pipe, you would switch to pressure mode — or even a three-stage pump mode if so equipped — all this while pumping from draft to meet those specs. If you have a good hydrant system with decent flows and pressures, you can supply much more than the flows and pressures you can from draft. However, the two mode selections (volume, parallel) or (pressure/series) work the same, whether from draft or supplied source.
WHAT NFPA chapters apply to fire apparatus?
Hundreds of chapters pertain to fire apparatus. There are far too many to list here. However, the following are the most commonly used NFPA Standards:
NFPA 1002, 2014 Edition; Standard for Fire Apparatus Driver/Operator Professional Qualifications
NFPA1071, 2011 Edition; Standard for Emergency Vehicle Technician Professional Qualifications
(Ernie note: Fire Mechanics/Emergency Vehicle Technician [EVT])
NFPA 1500, 2013 Edition; Standard on Fire Department Occupational Safety and Health Program
NFPA 1901, 2009 Edition; Standard for Automotive Fire Apparatus
(Ernie note: This is the minimum standard by which fire apparatus are to be built.)
NFPA 1906, 2012 Edition; Standard for Wildland Fire Apparatus
(Ernie note: addendum to NFPA 1901)
NFPA 1911, 2012 Edition; Standard for the Inspection, Maintenance, Testing, and Retirement of In-Service Fire Apparatus
(Ernie note: this is the standard by which your fire mechanic/EVT performs the tasks of inspection, maintenance, testing and retirement of fire apparatus and includes Out-of-Service (OOD) criteria.)
NFPA 1912, 2011 Edition; Standard for Fire Apparatus Refurbishing
(Ernie note: there is a huge difference between refurbishing an older apparatus from the original NFPA Standard when built, Level I and refurbishing/rebuilding to original specifications at time of build Level II.)
Can you explain the two types of refurbishing being performed by various manufacturers?
As listed in the NFPA 1912, 2011 Edition, a Level 1 refurbishing of the apparatus is performed to meet all current requirement of applicable chapters of NFPA 1901, 1906, or 414. A level II refurbishing shall meet the requirements of applicable chapters of the edition of NFPA in effect at the time of original manufacturer. The extensive listing of testing and qualifications to meet the original manufacturing specifications are extensively listed in chapter six.
What are the benefits of having a medium duty chassis versus light duty chassis for medic units?
Ask this question of 10 different agencies and you will get four different answers.
In favor of the medium duty chassis (Ford, International, Freightliner, GMC HD) and assuming you have researched well and written well thought out specifications: fewer breakdowns, greater longevity, larger capacity box with more work and storage room, higher horsepower and torque motors, you sit much higher in the cab and have a greater field of vision, and you may find that the operators have a tendency to slow down more through turns.
Cons regarding the medium chassis: harsher ride, but is getting better as ambulance manufactures learn more.
For agencies that run fewer calls per year, the light duty chassis may work out well and last the desired time frame to replacement.
(Ernie note to prospective ambulance purchasers: There is a new rear suspension system specifically designed for smoother rides for your applications. The product is called “Liquid Spring” from Liquid Spring Technologies of Lafayette, Indiana. Check them out at: www.liquidspring.com. Ask for a ride evaluation on an actual ambulance chassis and see the difference. Uncle Ernie has done the demo ride and it appears to be what the ambulance service has been looking for. Make your own evaluation and decision.)
What are some different auxiliary braking systems?
I think your old Uncle Ernie has addressed this in the past. Let’s try it from memory.
Engine compression brake (AKA Jake Brake)
Eddy current electromagnetic driveline brake (either focal or chassis mounted)
Integral transmission hydraulic retarder
Exhaust brake, any of which can be accompanied by the later engine designs with a variable pitch turbocharger, which can assist by blocking exhaust stream.
Per NFPA 1901, any apparatus greater than 36,000 GVWR must have an auxiliary braking system and NFPA and Uncle Ernie suggest installation of the an auxiliary braking system on apparatus of less than 36,000 GVWR.
Is there a life span on tires for fire apparatus? They sometimes don’t wear out.
Trust Ernie on this: Tires DO wear out. In days past, long past, tires were made of natural rubber, which resisted breakdown and failure for long periods of time. However, tires did not last long distances. As roads improved and tires were required to go very long distances before wear out, the old natural rubber tire had to improve. Today, tires are a by-product of petroleum and are designed to go great distances to wear out (80,000 miles for cars and up to 120,000 miles for heavy trucks in interstate travel. The issue is that the tire petroleum compounds break down quickly. To that end, responsible tire retreaders will not recap a tire greater than five years old and tire manufacturers and NFPA (1911, 2009 Edition; 7.3.4 states that, “Tires shall be replaced at least every seven years or more frequently when the tread wear exceeds state or federal standards as determined by measuring with a tread depth gauge.” For agencies that rarely respond, the tire at seven years of age may appear good to go, but that is not the reality. For agencies that make a large volume of calls per year, they may replace tires two or three or more times per year, due to tread wear out.
Is a pump testing trailer actually compliant or just convenient?
Actually, it is a convenience and meets NFPA standards for agencies that forego the annual testing procedure due to the burden of travel expense and labor expense or any other reason. This type service is an answer that does comply with NFPA 1911, 2012 Edition; 18.6.2, under Alternative conditions: If it is impractical to provide all the conditions specified for annual pump testing in Sections 18.3 and 18.4, the AHJ (Authority Having Jurisdiction) shall be permitted to authorize testing under other conditions.
(Ernie note: if a testing trailer system is utilized, it shall be consistent year-to-year pursuant to Section A 18.6.)
Pump packing mechanical versus rope style, any preference?
Having had both in my fleet, I prefer the mechanical seal of today. Early mechanical seals on large volume pumps did not have the longevity I desired. Today, much of the mechanical seal longevity issues are gone. However, when an operator runs out of water and continues to run the mechanical seal dry, it will quickly overheat and damage itself. If the operator realizes that the pump is dry and then induces cold water onto the seal ceramics, it can easily shatter the seal and require replacement. If given a choice between the rope style, plastic injection type, or mechanical seal, Ernie would choose the mechanical seal.
(Disclaimer: Uncle Ernie does not sell any product and is simply the purveyor of available information.)
— Ernie questions answered by Anthony D. (Tony) Bulygo.