Swimming pool engineering

The pool at East Island Farmhouse has undergone numerous repairs and upgrades since we purchased the premises in 1995. These works warrant documentation, since they represent the collection of large amounts of information and practical experience.
     The most recent major upgrade (Aug. 2017) was the installation of an array of evacuated tube solar panels on the pool building roof. This heating system consists of 6 × 30 tube panels, with a peak output of 11.1 kW, and a heat-dump in case of pool curculation failure. The system appears to be working well (Feb. 2017) and is described in a a separate article.

Backstory .
 Solar heating system .

Warning A note on the Sunvic SZ 2301 zone valve (2020-6-21).
The heating system for the East Island pool is somewhat complicated, and a few years ago it developed an annoying fault that was difficult to trace.  The problem was that the oil boiler was always on, even when no heating services were required.  The solution, for a long time, was simply to turn the boiler off at the thermostat, but the recent installation of a high efficiency replacement unit prompted investigation of the problem.  It turned out to be due to a Sunvic SZ 2301 zone valve controlling the feed to a radiator in the pool corridor. This valve was issuing a boiler request even when de-activated.
     I contemplated buying a new valve actuator head, but these are stupidly expensive and have a reputation for unreliability.  So, instead, I dismantled the device to find out what was wrong (a security Torx TR10 screwdriver is required).  It turns out that the boiler request microswitch is mounted on a couple of pathetically flimsy pins protruding from the ABS back-plate.  The switch is also loose on the pins for about 2 mm of up-and-down movement, increasing the stress on the plastic.  I estimate that the valve might undergo someting in the order of 1000 operations before shearing-off one of the pins, which would seem to be in keeping with the user-reported MTBF of 2 to 3 years.
     Buying an identical replacement for a part designed to fail is not a solution.  Instead, I carefully marked the location of the sheared-off pin with a centre punch and drilled a 2 mm diameter hole in its place.  I then secured the microswitch with an M2×0.4 screw (12mm long excluding head) and a nut.  This arrangement does not allow any movement on the backplate and should last for many years.

Web links

Bimetallic corrosion. NPL guide to good practice in corrosion control.

Pool water treatment advisory group.
Hanovia UV water treatment technology.
Blue lagoon UV-C water purification.

Clear PVC pipe - Plastic Pipe Shop.
 PVC pipefittings -
Effast air-release valve - Collister & Glover.

Swimfix - Supplier of pool equipment, parts, consumables and services.

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