Using a Plate exchanger to cool a 175 Changfa

[Tom Reed]

There's a small 120vac circ pump on my co-gen system that is controlled by a snap switch. It runs continuously once the engine is warmed. There's never been an issue with shut downs while the motor was on. IIRC it's a Grunfos 3 speed pump.

[Jens]

So the disadvantage I see to using a pair of pumps, is automatically powering them, and if I wired them to the ST head, wouldn't they stay wired when the motor winds down, and kill the residual magnetism ?  I don't have a 12V circuit, just the 250 out from the ST head.  I have 120Vac in the shed, but that's another switch to remember, both ON and OFF.  Would a snap disc thermostat be a feasible route to use ?  Attached to the engine side of the heatex, set for 180F ? 

I don't know about the ST heads but my Marathon head never had any demagnetization issues. I forgot all about that aspect in my previous post. On the other hand, if you have an automatic shutdown, you can just run the pumps via a relay the drops out as soon as a shutdown is initiated.
Circulator pumps are cheaper for 240 volts from fleabay - that's how I got mine for cheap

I would not use a snap disc for a critical item such as auto shutdown but I would use a snapdisc as a secondary safety (for example attached to the engine head).
In a non critical roll, a snap disk would be fine - for example to turn on a radiator fan when coolant gets up in temperature. For the normal shutdown process I would only trust something like a Murphy temperature gauge with contacts so you can set the trip temperature.

[mobile_bob]

my st head has never lost residual magnetism, no matter what load i shut it down with
and sometime it has been shutdown with a full load resistive bank attached.

now having said that, the head often takes several seconds to excite and come back up online
it will often run at rated 1800rpm for maybe 15 to 20 seconds before the needle starts to swing back up to full voltage. once it starts to move up it gets there in a second or two.

if you put the pumps on a relay where the st head voltage has to hold the coil engaged, the relay will drop out long before the voltage gets to zero, that ought to save those st heads from losing residual magnetism that are affected by loaded shutdown conditions.

fwiw
bob g

[Ronmar]

My breakers are on the doghouse, so it is a simple matter to shut them off when I shutdown.  The pump that is on my secondary is plugged into the outlets on my loadbank panel and it receives power as soon as I put the breakers on after startup.  My secondary pump is the smallest Taco they make, a 004 I think.  I think it pulls 25-30 watts when running, so a pretty tiny load.  It pumps way more than needed to remove the heat at the temps I am running, 120F on the secondary regulated by an outboard motor thermostat.  A snap switch on the side of the head should work fine for pump control.