ausmini :: View topic - mini water pump bypass hose

OK thanks, I found it that time - a reference to cavitation leading to erosion / corrosion? That it?

I would have to disagree. The design of the water pumps in minis is that of a centrifigal pump. There are a lot of variables in the design of these pumps and depending upon these variables the optimum shaft speed is between 900 and 3000 RPM. Some can run faster. At slower than optimum speeds the fluid flows at a lower rate. At speeds not far above the pump cavitates. Also, the correct method of shuting off flow from a centrifigal pump is to shut off the outlet to i) ensure that the impeller and seals still have 'head' and ii) to avoid cavitation. This is done in a car engine by way of the Thermostat. Further the ID of the by-pass fitting on the pump is only about 8 to 10 mm and the outlet fitting is about 22 mm. The flow rates between the two are chalk and cheese, not to mention the flow dynamics caused by having the by-pass coming off at hard right angle. Any 'flow' through the by-pass would be very very small indeed.

Regarding the optimum shaft speeds, being probably around 3000 rpm for the mini water pump, this is why we fit larger diameter pulleys on the pump for race motors, because they constainly run at higher rpm it is necessary to slow the pump to prevent cavitation.

Author:	miggy [ Mon Oct 12, 2009 5:29 pm ]
Post subject:	mini water pump bypass hose
Hi, I changed my water pump on my 998 clubman and when I removed the bypass hose I found the pipe that the hose clamps onto the head was so corroded most of it came out with the hose. As there is only a small part of it still there I can't get enough purchase on it with the new peice of heater hose and clamps and it leaks. How should I repair the pipe from the Head? Is it a screw in like this: http://www.minisport.com/acatalog/info_12A2075.html Otherwise it it easy to blank off? Any help appreciated. Cheers

Author:	Wombat [ Mon Oct 12, 2009 5:56 pm ]
Post subject:
Get one from the Doc - he makes them out of brass and won't corrode

Author:	drmini in aust [ Mon Oct 12, 2009 6:07 pm ]
Post subject:
PM me to get a brass one. Will never rust out. Price $14 including post. You will probably have to remove the head to get the old threads out if the old nipple is badly corroded. Thread is 5/8-18 UNF. I drill them out 9/16" on the bench drill, then run a 5/8 UNF tap in to peel the remains out.

Author:	GT mowog [ Mon Oct 12, 2009 6:23 pm ]
Post subject:
Not to take any coin away from the Doc, but I'd suggest blanking it off. It doesn't really serve much purpose (in Oz) and by blanking it off you can get rid of the pesky little hose that rots out. Nice touch Doc, brass

Author:	drmini in aust [ Mon Oct 12, 2009 6:55 pm ]
Post subject:
GT mowog wrote: Not to take any coin away from the Doc, but I'd suggest blanking it off. It doesn't really serve much purpose (in Oz) and by blanking it off you can get rid of the pesky little hose that rots out. Nice touch Doc, brass Explain to me then how the water circulates in the block and head during when thermostat is closed.. with NO bypass. In summer anyway, when heater tap is off. If you plug it, I would drill a few 3mm holes in the thermostat body. Metros etc in UK that had no hose, had a sandwich bypass plate under the thermostat... with an even tinier hose. Use a bit of decent (USA made) heater hose (like Cooper S has), not that stupid little ex-Morris Minor convoluted hose that are rubbish these days. Heater hose lasts for yonks.

ausmini https://www.ausmini.com/forums/

mini water pump bypass hose https://www.ausmini.com/forums/viewtopic.php?f=2&t=57877	Page 1 of 3

Author:	GT mowog [ Mon Oct 12, 2009 7:33 pm ]
Post subject:
The thermostat opens (even a small amount) and the water circulates. Even when they're closed they don't seal. Here in Oz, the ambient temp is nearly always high enough that the thermostat will always be open some amount. In colder climates, it still will work satisfactorily as with the thermostat 'closed' the engine temp will rise sufficently to open the thermostat and circulate coolant. After all that's part of the function of the thermostat. I have done this on countless cars with no adverse effects. Possibly the only drawback is when filling the system from cold takes longer and needs to be re-visited a couple more times. There are many many 'other' engines that do not have any type of by-pass system.

Author:	drmini in aust [ Mon Oct 12, 2009 9:02 pm ]
Post subject:
Anyhow miggy if you want a brass bypass adapter here's what mine look like. They are made from hex bar, so you can actually undo them again...

Author:	miggy [ Tue Oct 13, 2009 8:33 am ]
Post subject:
Ill send ya a pm Dr mini. cheers

Author:	winabbey [ Tue Oct 13, 2009 9:32 am ]
Post subject:
See this thread which talks about the effects of removing the bypass hose. http://www.ausmini.com/forums/viewtopic.php?t=57339 This is the blanking sleeve that can replace the thermostat: http://minispares.com/Product.aspx?ty=p ... %20SLEEV...

Author:	GT mowog [ Tue Oct 13, 2009 4:49 pm ]
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winabbey wrote: See this thread which talks about the effects of removing the bypass hose. http://www.ausmini.com/forums/viewtopic.php?t=57339 Mmmm, sorry, this maybe the wrong link. It did have some info on removing the by-pass but not on the effects. Could you have another look as I am interested to read up on that.

Author:	winabbey [ Tue Oct 13, 2009 5:01 pm ]
Post subject:
GT mowog wrote: winabbey wrote: See this thread which talks about the effects of removing the bypass hose. http://www.ausmini.com/forums/viewtopic.php?t=57339 Mmmm, sorry, this maybe the wrong link. It did have some info on removing the by-pass but not on the effects. Could you have another look as I am interested to read up on that. Several posts in that thread commented on what would happen if the bypass hose was removed (and the holes plugged) with the thermostat still in place. That's what I meant by 'the effects'.

Author:	GT mowog [ Tue Oct 13, 2009 7:03 pm ]
Post subject:
OK thanks, I found it that time - a reference to cavitation leading to erosion / corrosion? That it? I would have to disagree. The design of the water pumps in minis is that of a centrifigal pump. There are a lot of variables in the design of these pumps and depending upon these variables the optimum shaft speed is between 900 and 3000 RPM. Some can run faster. At slower than optimum speeds the fluid flows at a lower rate. At speeds not far above the pump cavitates. Also, the correct method of shuting off flow from a centrifigal pump is to shut off the outlet to i) ensure that the impeller and seals still have 'head' and ii) to avoid cavitation. This is done in a car engine by way of the Thermostat. Further the ID of the by-pass fitting on the pump is only about 8 to 10 mm and the outlet fitting is about 22 mm. The flow rates between the two are chalk and cheese, not to mention the flow dynamics caused by having the by-pass coming off at hard right angle. Any 'flow' through the by-pass would be very very small indeed. Regarding the optimum shaft speeds, being probably around 3000 rpm for the mini water pump, this is why we fit larger diameter pulleys on the pump for race motors, because they constainly run at higher rpm it is necessary to slow the pump to prevent cavitation.

Author:	GT mowog [ Tue Oct 13, 2009 7:40 pm ]
Post subject:
Doc, have you ever though of offering brass plugs as well as adaptors?

Author:	richarde [ Wed Oct 14, 2009 6:49 pm ]
Post subject:
GT mowog wrote: OK thanks, I found it that time - a reference to cavitation leading to erosion / corrosion? That it? I would have to disagree. The design of the water pumps in minis is that of a centrifigal pump. There are a lot of variables in the design of these pumps and depending upon these variables the optimum shaft speed is between 900 and 3000 RPM. Some can run faster. At slower than optimum speeds the fluid flows at a lower rate. At speeds not far above the pump cavitates. Also, the correct method of shuting off flow from a centrifigal pump is to shut off the outlet to i) ensure that the impeller and seals still have 'head' and ii) to avoid cavitation. This is done in a car engine by way of the Thermostat. Further the ID of the by-pass fitting on the pump is only about 8 to 10 mm and the outlet fitting is about 22 mm. The flow rates between the two are chalk and cheese, not to mention the flow dynamics caused by having the by-pass coming off at hard right angle. Any 'flow' through the by-pass would be very very small indeed. Regarding the optimum shaft speeds, being probably around 3000 rpm for the mini water pump, this is why we fit larger diameter pulleys on the pump for race motors, because they constainly run at higher rpm it is necessary to slow the pump to prevent cavitation. I partially agree with this. Running a pump at higher than design speed is not always going to cause cavitation though. It depends on what is on the suction side of the pump. Many pumps can be purchased in 1500rpm (1450rpm) and 3000rpm (2900rpm) speeds but are the same pump. Getting the 1500rpm version and speeding it up won't do anything to the pump. Also, variable speed drives allow a pump to be run at 110% of original speed. It depends a lot on the pump design and the flow path (and the static head on the pump). Slowing the pump down on race engines may be due to cavitation, but would also be done to reduce the power absorbed by the pump. Basically cavitation is when the pressure in the pump drops low enough that the water begins to boil. Blocking the suction can cause this, or incorrect pump selection. You say "Any 'flow' through the by-pass would be very very small indeed.". I work in the water/wastewater industry so I have a fair bit of experience with pipes and pumps and if you do the calcs you often find that putting an orifice plate or partially closing a valve doesn't have a huge effect on flow until you start to get the valve to the last 25% or so of travel. The bypass hose on the Mini may still pass a fair bit of water. If you run a centrifugal pump with zero flow the radial force on the pump shaft is a lot higher than if there is some flow, so the seals and bearings can wear out quicker. I suspect this wouldn't have a huge impact on pump life for a car water pump though, as they are probably a fairly robust design. I would probably lean towards leaving the bypass there, since it is there to start with (or drilling the thermostat as the Doc suggests), but it would probably work fine without it and I don't think it would have a huge effect on water pump life. There are more important factors anyway, like making sure you get a decent pump instead of one with a pressed steel impeller.

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Author:	GT mowog [ Wed Oct 14, 2009 7:20 pm ]
Post subject:
Hi Richarde, thanks for your input, I'll chew that over. I too have a bit to do with testing pumps, but more so on the large end, the largest did 5000 lts per sec (you could walk through it) but that's another story for another day. I guess the best way to resolve the by-pass flow rate issue would be to test it for flow rate.