Re: [Amel] Domestic Water pressure switch.
In answer to your questions:
Q. 1. Is the pressure tank at the pump one that has a bladder?A. If this is the original Amel accumulator tank (stainless) attached to the pump, then yes it does have a bladder. Almost accumulator tanks will have a air pressure valve on one end. It looks like a valve stem for an auto or bicycle tire tube.
Q 2. How does the additional reservoir/tank above the water heater add to the system?A. I am virtually positive that the accumulator tank on the hot water heater side is to allow for water expansion as it heats. Many hot water systems in industrial and residential systems have similar accumulator tanks.
Q 3. What are the common problems you've found with our systems?A. I have found the system to be very good. My biggest obstacle was understanding British Straight Pipe Thread (no taper to the thread and depends on sealant to achieve a seal) as opposed to NPT (National Pipe Thread) which are tapered pipe thread and achieve a seal by means of interference fit of the threads. I have made peace with BSPT and have actually grown to like it better than NPT, especially when it comes time to disassemble something.
The only real problem I had was the hot water side accumulator tank rusting through at the neck fitting. This occurred twice and has been reported by others. I believe it was a manufacturing defect.
Q 4. Since our pressure tanks are small compared to the ones featured in the site at Eric's link, I'm not sure how long it should be between pump cycles.Â It's always been 10-12 seconds on my boat until now, but I'm not sure that's what it should be.A. I don't have a firm answer for this. The water pump originally supplied by Amel is a centrifugal pump and not a positive displacement pump. How long the pump runs depends on the setting of the pressure switch on the pump and only slightly due to wear of the impeller or the pump cavity. As you mentioned, the cold water accumulator is small and so cycling will be fairly frequent. Larger accumulators would cycle less frequently but when the pump comes on it will run for a longer period of time to "fill" or charge the accumulator tank.
Q. The pump that was on my boat when I got it wouldn't turn on at all, so I replaced it with a spare that had been purchased by the original owner.Â I haven't had any problems for 5 years now until now.A. I think your experience is pretty typical. I have gone through two pumps in 12 years. One failure mode I experienced was the woodruff key that secures the pump impeller on the motor shaft was made of mild steel and corroded away, This left the bronze impeller unable to turn with the stainless motor shaft. I fabricated stainless woodruff keys from stainless bar stock and haven't had a recurrence. (woodruff keys are the semicircular keys that fit in a groove in the pump shaft and affix the impeller in place against rotational counterforce).
Hope this helps,