Hot water woes

A recent episode where the 170l gas storage hot water service relieved itself through the pressure / temperature relief valve sent me on a quest to understand the problem.

At the time, a ‘full rate’ discharge of 95° water was holding the valve open, and even with the gas turned off, the flow continued for some time until I closed the water isolation valve to let the system cool down.

So, was this simply a thermostat failure, temporary or permanent, or perhaps the result of ‘stacking’.

Stacking is caused by repeated very short draws of hot water, which cool the bottom of the tank near the thermostat, triggering heat input which can cause the top of the tank to reach temperatures considerably higher than the set point of the thermostat.

Another question that was of interest in choosing a replacement if needed, was how much heat is lost from the heater, what is the running cost of heat leakage alone.

Heat leakage

The heater was allowed to reach ‘normal’ operating temperature and stabilise, and the gas valve was closed which would allow the unit to cool.

A variation on my IoT water tank telemetry project was configured to use a type K thermocouple and 4-20mA converter to provide a temperature logger, a type K thermocouple was inserted between the insulation blanket and tank at the top of the tank. The 4-20mA converter does not incorporate cold junction compensation, but the logger incorporates an ambient temperature measurement facility which will be used for approximate compensation.

Above is the improvised data logger setup. Continue reading Hot water woes

A mid life kicker for the 2500VA 230V 50Hz genset

About 10 years ago I purchased a 2500VA genset on eBay for about $250 incl delivery. It turned out to have wiring problems behind the control panel, and required an hour’s work to fit some new wires and terminations and make it safe. The seller refunded $80 as compensation.

It has what appears to be a genuine Honda GX160. Now I bought it with I must say a great deal of skepticism, but having worked on many Chondas (Chinese Honda ‘clones’) this is undoubtedly a class above, and I think on all the evidence available, it was a Chinese manufactured Honda destined for the domestic market. Continue reading A mid life kicker for the 2500VA 230V 50Hz genset

Holzforma / Farmertec G372XT chainsaw – initial evaluation

I purchased a Holzforma G372XT chainsaw, it is a Chinese clone of the now discontinued Husqvarna 372XP X-TORQ. It is a relatively new technology carburetted engine without introducing electronic auto tune, a 20 year old design.

There are plenty of online discussions about the 372XP X-TORQ overheating, hot seizures, and pics of blued big ends, scored pistons and bores etc, so whilst the design achieves quite high power output for 71cc, one is warned to pay attention to mixture, fuel quality, and lubrication. This might be an engine that should not be used with other than full synthetic two stroke oil. Continue reading Holzforma / Farmertec G372XT chainsaw – initial evaluation

The mower appears affected by Ethanol

I have a Toro ride-on mower which ran out of fuel when it was just a couple of years old, perhaps 50 hours on it. Okay, so that is going to happen with failure to check fuel level before starting… but the problem was that when the tank was filled, it would not start, the petrol pump would not self prime even though the suction head was very small with a full fuel tank.

Mindful that long cranking is very hard on batteries, I used the starter sparingly in short bursts with cooling off time. Nevertheless, the battery went open circuit.

So I replaced the battery and primed the pump by hand… and all has gone well for some years… until last week, I ran it out of fuel, duh!

Same problem, when the tank was filled, the pump would not self prime.

The machine has a problem that needs to be fixed.

The inline filter was checked, and fuel flowed though it quite well by gravity. This time, I primed it by hand early in the process and got on with mowing. This was probably not a vapor lock problem, everything was quite cool by the time I fueled the machine. Continue reading The mower appears affected by Ethanol

The mulcher appears affected by Ethanol

I have a chipper / shredder that has a Briggs and Stratton 6.5hp (~5kW) Intek I/C 206cc engine on it.

On a recent routing maintenance inspection, I dropped the carburettor bowl to look for signs of Ethanol damage (mainly corrosion). During that inspection I noted that the bowl gasket was hardened even though the engine is only 13 years old, and that a stain on the mulcher body hinted a fuel leak even though the bowl exterior seemed dry on test..

The machine is usually stored with the petrol cock off, so the opportunity for a needle / seat leak would be during a day’s yard work where the petrol cock is on for hours but the machine is run for a lesser time.

A pressure test might provide a firm diagnosis.

A piece of silicone tube was connected to the carburettor in place of the normal fuel hose, a little petrol added to the hose with a pipette, and then a sphygmamometer used to pressurise the hose.

Above, the test in progress. The fuel level in the hose can be seen about 30mm from the end. The pressure is leaking down quite slowly, the leak is not fast enough to upset engine operation (by flooding or even an over rich mixture) but it might well result in dilution of the crankcase oil when the engine is left standing. It needs repair. Continue reading The mulcher appears affected by Ethanol

Chinese chainsaw review – SX25 #1

When we moved to this place in 2009, I could see the utility of a ‘aborist chainsaw’, or ‘top handle chainsaw’.

I bought a cheap Chinese 25cc jobbie, in fact it was so good I bought a second for spares.

SX25#1

This saw had seen off 6 chains by 2021 and forced by some reliability issues, I decided to replace it with the spare and repair it at my leisure (parts from China are real slow). It has had a good life, usually warmed up before being gunned up to WOT to avoid cold seizure. Continue reading Chinese chainsaw review – SX25 #1

Small 2-stroke engines and popoff pressure

This article explores the physics of fuel metering in a typical small diaphragm carburettor (carburetor to some) as used on small 2-stroke chainsaws, leaf blowers, brushcutters etc.

The discussion following is in terms of absolute pressure, and it is assumed that atmospheric pressure is 100kPa. ALL pressures are absolute unless stated otherwise, to find gauge pressure, subtract 100kPa.

Above from Zama is a cross section view of the metering chamber of a typical butterfly carburettor. The metering lever pivots on an axle (1), the distance from the axle to the needle (2) is 3.5mm, to the spring (3) is 3.5mm, and to the contact to the metering diaphragm (4) is 8mm. The needle seat is 0.55mm diameter. Continue reading Small 2-stroke engines and popoff pressure

Small engines and green fraud

Recent weeks have seen some catch up work on maintenance of small engine yard equipment. There are 22 engines in all, 6 4-stroke and 16 2-stroke.

For some years, ‘green’ measures implemented by government meant that ordinary unleaded petrol (ULP) was not available retail, one had to use E10 (ULP with 10% Ethanol).

Greens claimed that at such low Ethanol, that the fuel was compatible with all existing and new engine equipment.

Diaphragm carburettors

Most of my 2-stroke small engines use so called diaphragm carburettors. These ‘all position’ carburettors are common on yard equipment like brushcutters, leaf blowers, chainsaws etc.

Above is a Chinese after market clone of a Zama ‘butterfly’ type (note the throttle butterfly) diaphragm carburettor that suits a Stihl BG85 and similar leaf blower. (This cost $15 inc shipping on Aliexpress.) Continue reading Small engines and green fraud

Replacing the crystal in a Seiko V158-0AD0 watch

I have a Seiko V158-0AD0 which works very well, and I recently noticed the crystal was scratched more than the case… so a strong hint that it is an ordinary mineral glass crystal.

Searching the net, I could find that the Seiko part number for the original crystal is 310P03HN0 which indicates a diameter of 31.0mm but it does not have the thickness encoded simply. I could not find any articles giving the thickness of the part… so measurement was needed.

Above, the original crystal measures 1.6mm. A ‘standard’ 1.5mm sapphire crystal should be just fine. Continue reading Replacing the crystal in a Seiko V158-0AD0 watch