oddballrovers Posted July 29, 2007 Share Posted July 29, 2007 Hi Everybody. Last night after a few beers at the local blacksmiths workshop we started to get inventious, and the question raised, can gear pump be ported? I do remember years back before the ZF pump came out on the 300TDI people used to do something to the old type pump. But here we are talking about larger pumps for ie winch or even hydrostatic drive off your toy. When one look at the pump it seems rather crude made and we thought; what would happen if we did enlage the out let by say 3mm it is about 12 and also did the same on the inlet or just did it on the inlet? Is this way off or does anybody know a bit about it. Kind regards Ole. Quote Link to comment Share on other sites More sharing options...
Bush65 Posted July 29, 2007 Share Posted July 29, 2007 Increasing the driven speed, increases the flow rate. The driven speed is often limited by cavitation caused be turbulence at the inlet port. The speed at which cavitation occurs could be increased if the inlet port is made larger and steps, corners etc, smoothed to reduce turbulence. The inlet line needs to be larger than the the delivery line, but often the inlet and delivery ports are the same size if the pump direction can be reversed. Quote Link to comment Share on other sites More sharing options...
Tobias Posted July 29, 2007 Share Posted July 29, 2007 Increasing the driven speed, increases the flow rate. The driven speed is often limited by cavitation caused be turbulence at the inlet port.The speed at which cavitation occurs could be increased if the inlet port is made larger and steps, corners etc, smoothed to reduce turbulence. The inlet line needs to be larger than the the delivery line, but often the inlet and delivery ports are the same size if the pump direction can be reversed. Since pumping is all about pressure differences. What about putting a (low) overvpressure in the tank? Would this prevent cavitation / allow a higher overspeed before cavitation is a problem? T Quote Link to comment Share on other sites More sharing options...
dollythelw Posted July 30, 2007 Share Posted July 30, 2007 I dont think thats feasible Tobias IMO the ratio between low and high pressure would either be too low to be of benefit or to high to be practical? - improving the flow efficiency of the system overall would be of a greater benefit, particularly the feed side (my coffee levels are low at the moment so this might be poorly thought out ) Quote Link to comment Share on other sites More sharing options...
Raumer Posted July 30, 2007 Share Posted July 30, 2007 Increasing the feed pressure won't affect when cavitation occurs. It's down to things like gear speed, shape of internal parts etc........ Have lots of problems with cavitation on the stuff I work on just at higher pressure (2500 bar plus!). Smoothing out sharp edges and basically improving the flow path will help. All of our important parts are honed to achieve this. HTH Ed Quote Link to comment Share on other sites More sharing options...
oddballrovers Posted July 30, 2007 Author Share Posted July 30, 2007 Hi Folks. So to sum it all up, it is all about avoiding cavitation, re, enlarging the ports is it only on the inlet there is any gain in smothing things out? Having thought about where and in what way to enlarge the inletport my idea is to make the port oval/wider but keep the diameter as the smaller dimension, is that a right thought? And then off course smoth out all sharp edges and so. But what then about the outlet is that the same? Kind regards Ole. Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted July 30, 2007 Share Posted July 30, 2007 At low pressure differences (ie not 2500 bar!) I think that feed pressure will have an effect on cavitation - hence why hydroelectric power station pumps are below the level of the lower lake (ie Dinorwig). However, it's a gamble to have a box full of hot pressurised oil behind your head I feel. Quote Link to comment Share on other sites More sharing options...
Raumer Posted July 30, 2007 Share Posted July 30, 2007 Higher feed pressure will help keep the system primed and will prevent air pockets. This will improve the system performance if there is already a problem. With a well set-up system there shouldn't be any problem and with the relatively low demands and output pressure you should only need a slight head to prevent this. Cavitation is caused by the collapse of pockets within the fluid. Very destructive, plucks material away from the surface. HTH Ed Quote Link to comment Share on other sites More sharing options...
Bush65 Posted July 31, 2007 Share Posted July 31, 2007 Higher feed pressure will help keep the system primed and will prevent air pockets. This will improve the system performance if there is already a problem. With a well set-up system there shouldn't be any problem and with the relatively low demands and output pressure you should only need a slight head to prevent this.Cavitation is caused by the collapse of pockets within the fluid. Very destructive, plucks material away from the surface. HTH Ed IMHO, the collapse of pockets within the fluid is the cause of the destruction. The cause of the pockets is the suction pressure dropping below the vapour pressure of the fluid. Quote Link to comment Share on other sites More sharing options...
Raumer Posted July 31, 2007 Share Posted July 31, 2007 Oops! It was late at night, tired etc............! Bush65 is completely correct and I'll go and hide under a bush for a bit! Ed Quote Link to comment Share on other sites More sharing options...
oddballrovers Posted August 3, 2007 Author Share Posted August 3, 2007 Hi Spoke to Magam contender yesterday, hi had succesfully been running a 3300 rpm pump at 4500 by force feeding it from the return with a presure regulator so that the feed presure was 40bar's, worth thinking off. Kind regards Ole. Quote Link to comment Share on other sites More sharing options...
simonr Posted August 4, 2007 Share Posted August 4, 2007 It does make sense that if the inlet pressure is increased, it will be more difficult for a cavity to open. Si Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 4, 2007 Share Posted August 4, 2007 Spoke to Magam contender yesterday, hi had succesfully been running a 3300 rpm pump at 4500 by force feeding it from the return with a presure regulator so that the feed presure was 40bar's, worth thinking off. That would heat the oil quite a lot I'd imagine, if most of it is recirculating back through rather than going back to the tank. Also depending on the system you'd need a (pressure) filter in the loop otherwise stuff could circulate round and round without being filtered. Quote Link to comment Share on other sites More sharing options...
oddballrovers Posted August 4, 2007 Author Share Posted August 4, 2007 That would heat the oil quite a lot I'd imagine, if most of it is recirculating back through rather than going back to the tank. Also depending on the system you'd need a (pressure) filter in the loop otherwise stuff could circulate round and round without being filtered. Hi Fridge..... I know but is was merely a sort off proff that it is the cavitation that is the problem, he ran a filter in the return to the tank so it was only that part that was filtered and then hi had a large oilcooler somewhere in the system. I would prefer to have it so that the components is either desingned to do the job or modifyed to do it. This guy is right now using a piston pump from VOLVO it wil cope with 5600 rpm and is then driven direkt on the crank, but the price tag is not nice almost 700£. Kind regards Ole. Quote Link to comment Share on other sites More sharing options...
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