How come certain pumps are advertised as 3800 LPM @ 1000 kPa, 750 LPM @ 4000 kPa, 380 LPM @ 6200 kPa which is saying more volume can be moved at lower pressures.
Its related to whats commonly known as a pump performance curve. Pumps can be optimised for different performance primarily by the shape and dimensions of the impeller, ie radius, thickness, vain spacing, vain curvature. All this results in a different pressure performance relationship, one coming at the expense of the other. Usually pumps are tuned for optimum performance/efficiency at one particular setting. While were not too fussed about efficiency its a very critical factor when your using pumps in your business to get a pump optimised to the pressure/volume required.
If you look at just about any of the pump suppliers web sites they have them (darley etc). Even domestic pumps like onga have them. Many of the performance curves just give the performance at max RPM. The pumps we use (and many modern electric industrial pumps) have variable speed so there is another dimension to the curve really making it a 3D surface. Then there are additional corrections required based on pump inlet pressure etc.
Firefighters are primarily interested in what volume they can get at hose rated pressures. So if the pump has been matched up with the correct motor/gearing it should be able to provide that particular volume at that particular pressure.
Let's keep it simple a fire ground is not the place for volumetric pressure this and that.
Many fire services think otherwise. Thats why REAL pumpers have all this instrumented and displayed on the pump panel and in some services they train members to a higher level of understanding.
While volunteers don't do it much these days its also useful for appliance design. I bet the Burnside crew have spent many an hour flicking through manuals to get the pump they think they deserve on their new appliance (lets call it 441a)
Its also a useful part of planning. Lets say you expect that there will be 5 air tractors flying in and out of a nearby airstrip, each with a 3000L load on a 6 minute turn around and your going to bomb all day long dawn to dusk. Is the current pump capacity at the field sufficient? Do you need a pump that a local farmer has offered? Do you need to ship one from Adelaide overnight? or just commit an appliance to sit there and have one less on the fire line?
On the upper end most large industrial fires would have a team of engineers calculating numbers and equations all day long. How much water is going on, how much run off will there be, how to contain it. If your putting so much water onto a ship how long till it sinks or becomes unstable etc etc. Firefighting is half art half science.
I like training that is real world, practical and easily understood
Trial and error can be an expensive and dangerous pursuit. Understanding is critical in what we do so we can adapt to the situation to optimise the outcome without having to try the other umpteen options.
In the fire service we should start off as recruits knowing how and progress to why. Most national accreditation based learning doesn't really progress beyond how as it is considered unnecessary. However failure to go beyond how results in lack of innovation as people just do things as thats the way things have always been. While not everyone has to go beyond how the majority should to some extent.
Most fireys I have ever met would struggle with most of the scientific explanations above"
Indeed but this doesn't mean they shouldn't be exposed to it from time to time even if they don't understand it fully. God forbid we should ever think and just trust that those higher up in the system are thinking for us.
