Fire Engineering Training Community
Friction Factor - Hose Lines
Hi all
I did some training in hydraulics with my crew yesterday. We placed an inline pressure gauge at various positions along hose lines of various configurations and flow rates. Our hydraulics training manual provides fireground friction loss figures. They basically state a figure, given as a pressure (kPa for us) for each length of hose at the various diametres. For example it states that a 45mm (1 3/4") will loose 150kPa per 25 metre length. We all know that this is dependant on flow, and these figures are based on our common nozzle flow of 475 l/m (125GPM). Our practical tests showed friction loss was much less. We were loosing just under 100kPa (13 psi I think) per length. When I played with the formula I discovered that the friction factor (co-efficient) was set at a figure (0.006 for our metric calculations). This has been the figure for many years, since we were using rubber lined canvas hose. Now that we use synthetic hose, I'm thinking that the interior surface may be more smooth, and the co-efficient of friction may be less. I can't find anyone who knows how these co-efficients are arrived at. Are they based on tests using gauges and made the subject of the equation? Or are there special science type people who work it out another way? I played with the formula and changed the co-efficient to suit our results, and it worked in every scenario. I know this may seem fairly insignificant, but if we are to emphasise the importance of hydraulic knowledge and provide information to our firefighters, I think we need to reflect reality and be accurate. The figures published in our manual have always been the subject of disbelief, based on practical experience. Can anyone provide me with any information on this?
Regards
Mike Dombroski
New Zealand
I did some training in hydraulics with my crew yesterday. We placed an inline pressure gauge at various positions along hose lines of various configurations and flow rates. Our hydraulics training manual provides fireground friction loss figures. They basically state a figure, given as a pressure (kPa for us) for each length of hose at the various diametres. For example it states that a 45mm (1 3/4") will loose 150kPa per 25 metre length. We all know that this is dependant on flow, and these figures are based on our common nozzle flow of 475 l/m (125GPM). Our practical tests showed friction loss was much less. We were loosing just under 100kPa (13 psi I think) per length. When I played with the formula I discovered that the friction factor (co-efficient) was set at a figure (0.006 for our metric calculations). This has been the figure for many years, since we were using rubber lined canvas hose. Now that we use synthetic hose, I'm thinking that the interior surface may be more smooth, and the co-efficient of friction may be less. I can't find anyone who knows how these co-efficients are arrived at. Are they based on tests using gauges and made the subject of the equation? Or are there special science type people who work it out another way? I played with the formula and changed the co-efficient to suit our results, and it worked in every scenario. I know this may seem fairly insignificant, but if we are to emphasise the importance of hydraulic knowledge and provide information to our firefighters, I think we need to reflect reality and be accurate. The figures published in our manual have always been the subject of disbelief, based on practical experience. Can anyone provide me with any information on this?
Regards
Mike Dombroski
New Zealand
Michael Dombroski
I'll keep that in mind about the hose guys. I got an email yesterday telling me that the're looking into it (bit like a mirror).
We have Hale QPAC mid mounted pumps. The outlets are on the side and the pressure sensor is about 2-3inches from the hose coupling. I'm assuming this would give an accurate presure reading from the specific outlet. The only thing in the way between the gauge sensor and the hose is the coupling. Interestly enough, the main presure gauge, which is straight from the discharge before the seperation into the 4 outlets, reads the same as the outlets(when fully open and flowing). I take that as meaning that the plumbing betwen the discharge of the pump and the outlet coupling is very efficient, with no losses evident. This would make sense, as the pump casing is right behind the outlets, and pipe work does not appear to be restricting in any way.
Following this discussion, I've decided to follow this up more vigorously. I've contacted our national fire engineering department, but still waiting to hear back. I'm going to try and get hold of an inline flow gauge and get some more accurate data.
Cheers for the help.
Mike D
Kirk Allen said:
Jul 27, 2010
John K. Murphy
Jul 27, 2010
Kirk Allen
John K. Murphy said:
Jul 27, 2010