Hi Todd.  It does sound like series is the way to go.  Tell us more about this flow meter.  If adding a second pump for a backup, you'll have to know immediately if the first one quits working.  I'm thinking that you will likely damage the engine, or at least lose a large amount of coolant if you don't get the second pump on ASAP.  Ideally, there would be a downstream pressure switch, or something hooked into you flow meter to turn on the second pump automatically.    

 

The flow meter is a Signet paddlewheel sensor. They are obsolete at the mill I work in but there was still one in mill stores :-). I did a quick Google search and couldn't find anything, but I'll look in the files at work tomorrow, we should still have info. I believe that they are also used as knot meters on sailboats. Apparently they were available with a "T" fitting to install in-line however we haven't stocked that item in years, so I made my own which is just as well as it allowed me to keep the weight down and customize it for my install. I'll try to remember to bring a camera to the airport. Unfortunately the transmitter for this is big, bulky & heavy, so I've designed something better. The sensor itself puts out a square wave which I will convert into a voltage using a frequency to voltage IC chip (store phoned to say it's here-pick it up tomorrow). I'll convert the voltage signal into a 4-20mA signal and feed it to a small LCD display salvaged from a broken transmitter, and viola... a small, lightweight display for my panel. Meanwhile I've been flying with the leads from the sensor plugged into a Fluke multimeter displaying a frequency signal. Full flow = 23Hz which translates to ~45l/m.

 

The other option is to just run them all the time, which is probably what I'll plan to do.  The plan would be to have a pressure sensor downstream of the pumps.  During pre-flight, before cranking the engine, I can turn each pump on by itself, and verify that I hear it, and that it increases the pressure.  Even with the engine running, you may be able to see a slight drop in the pressure when turning the pumps off one at a time.  Of course, to see this... (whining about not having an EM-2 deleted) :-) 

 

Tonight the weather was crap so I didn't fly, but changed out the water pump, as today I gave it a real good going over to ensure it wasn't going to have any problems. Tomorrow I will fly with it to ensure that the flow numbers I see are comparable to the numbers I  was seeing with the old pump. Then I will install the old pump as a spare in series with the new pump and measure flow rates with it on & off to determine how much of a restriction it is when off and how much extra boost it can generate when off. Unfortunately the shaft is not accessible when in operation as I'd like to clamp it to ensure it doesn't freewheel when off in an effort to simulate a seized pump to measure flow restriction. I would have to clamp the impellor internally... possible but time consuming to keep refilling the coolant system... I think I'd rather fly off the hours:-). If the series arrangement doesn't prove to be feasible, I will try my T/flapper valve in a parallel arrangement. I'd much rather do this in series if it works as there is less weight and complexity. If it works well, then I will order another EWP along with a thermal switch from Leon. I have to return this original EWP for warranty inspection even though it now works well.

 

FWIW, this is the same philosophy that I use with my fuel pumps.  I check them individually as a pre-flight item, then run them both during flight.  My reasoning for this is to virtually eliminate the possibility of an in-flight fuel pump emergency.  I'd MUCH rather find out that one of my pumps has died while I'm safely on the ground, than to experience the anxiety of having the engine quit in flight.  The other plus is eliminating emergency checklist items.  If all your backup systems are already running, and the engine quits, you might as well just concentrate on landing dead stick.   The only downsides are a bit more current draw, and wear and tear on the pumps.  If the alt fails, I'll turn off one fuel pump, and one EWP to save some energy.  If I have to replace the pumps within a few years, big deal.  It'll be the cheapest thing I've done on this plane :-)  

 

I think you may find that by running both pumps all the time that you will have a very cold engine on descent. Yesterday as the ceiling was very low I couldn't do anything but circuits so I did T&G's for 2.5 hours. As I wanted to avoid the localized boiling issue, I just left the pump on bypassing the controller for the entire flight. I found that it was below 60C most of the time, with peak temps on full power climb to 1000AGL at 80C. Last week during my descent from 13000 to circuit height, the controller was at minimum flow to maintain temp at 85C. My plan is to keep the primary pump on the controller with the ability to bypass the controller (see attached wiring diagram- option 2) with the secondary pump controlled by a thermal switch set to 95C. In the event of a pump failure, rising temps will automatically start the secondary. In the event of a extended full power climb it will also kick it on, however I don't know that additional flow will reject more heat. If it doesn't then I know that my coolers are operating at their capacity. Secondary pump will also likely be used to cool down heat soak after shutdown.

 

 

I figure the pump itself is the majority of the weight.  The housing is only supposed to weigh about 3.5 lbs, maybe 4 - 4.5 lbs with the bolts.  My current thinking is that I won't save that much weight by removing the water pump housing, especially since you have to add an adapter fitting for the water flow to the block, along with an alternator mount of some type.  I'm going to look into just covering the water pump hole with a plate, and keeping the housing for all of it's other uses.  This realization was the key to allowing me to go ahead and order the EWP's.    

Take that bulky, heavy pump housing and throw it into the air, if it comes back down get rid of it and build a lighter, compact adapter:-) Seriously, it made a far neater installation without it. I also moved my alternator to the side, so I needed a new mount anyways. This was easy to make. Without the need for waterpump belts, I took the opportunity to simplify this as well, finding a serpentine pulley for the engine to match the one that came on my Geo alt. As I mentioned in another e-mail, a header tank is required, which will be easy for you to make with your new found welding skills. Removal of the pump will make it easier to install this.

 

So now, I have a big space behind the radiator, with full access to the end of the rear tank.  I also have no water pump.  What if I make the rear tank two separate tanks, just like the front tank is?  Now, it's effectively two radiators, side by side (take note evap guys).  The plan, is to put the two EWPs in series, in the empty space behind the radiator.  I would draw water from one of the rear tanks, and flow it back into the other tank, completing the circuit.  

 

I LIKE IT ! It sounds good to me. This will help with several things. Foremost is that it will help your forward CG.  It will solve your space issues and it will put the pumps in a cooler area.

 

Cheers,

Rusty (I hear sirens...and why are the sleeves so long on this coat)