Category Archives: Miscellaneous

Most essential if you want to dig a well: gravel pump design

The key tool for sinking a well (unless you want to climb in and dig it out) is a device called a plunscher, or a gravel pump. A punscher is a simple metal pipe, with a rubber flap (valve) at the bottom, and it will fill with sand when pulling it up quickly. This has to be done with enough speed to suck in sand, and you can add water to the well to get this done quickly (plunscher only works when submerged – at least mostly – in water). While this works well for sand and small gravel, the more efficient tool is a gravel pump – essentially a plunscher with a piston inside that will actively suck-in the sand from the bottom of the pipe. The piston will lower again under its own weight, and by repeated pulling it gravel pump will fill with sand and gravel quickly.

This is the setup, you can see the blue rope, make sure to use a good and strong rope, because the forces involved are quite substantial and sand will wear down these ropes, so better to exchange them from time to time in case you want to dig multiples wells.

First modification, a washer mounted in the middle of the rubber flap, it ensures better tightness and valve action. Some plunschers have this feature already from the supplier. Better to use some 4 mm fibre-reinforced NBR rubber.

The mounting screws are difficult to reach, so I mad an extension from a piece of wood…

The weld quality of the plunscher wasn’t all that good, but well, this is not a rocket engine, but a tool fabricated to a certain (rather moderate price tag). This price tag is also the reason why you wouldn’t directly by a gravel pump: a good gravel pump will set you back 150 EUR, whereas a plunscher can be obtained for 45~50 EUR. And, surely, it is more fun to do some modification yourself rather than buying all the expensive tools right away.

This is the modified plunscher, you can see the piston, and the cut-out.

The piston needs to have a valve action as to allow the piston to sink at moderate speed, but obtaining good vacuum when pulling the rope. I also tried to use two ropes: one for the piston, one for gravel pump case, but these ropes get entangled and there is no need for such ropes: the weight of the pump will keep it down, if you just pull with the right force and speed.

The piston needs to maintain some clearance from the wall, otherwise, it will get stuck with small stones, etc.

As a seal, I used leather from an old school bag, very firm and thick leather, and a somewhat smaller rubber disc (fairly hard NBR rubber). This worked well with no significant wear. The leather can be made such that there is almost no gap, for example, 1 mm, to ensure strong suction for fine sand. If you have coarse sand, probably you can also work with a larger gap or worn piston seal, you just need to pull the rope more often. I generally recommend to keep the gap small unless you run into some trouble with specific gravel or some particular sand or stone.

At the bottom, for the last meter, I attached a serrated, rather dangerous-looking teeth ring, to cut into the ground and loosen the sand. It worked marvelously. Generally I can recommend to keep the well flooded as much as possible by adding water all the time, then no sand will flow into the pipe if you hit a somewhat “liquid” layer. I probably kept the water level at least 50 cm above the water table.

The rope needs to be mounted such that the piston cannot be pulled out completely, this needs to be adjusted properly. Sure you could also weld a guide ring or similar for the piston, but it worked out very well with the more “wobbly” piston, the vacuum is strong, and the extraction of sand was more limited by the nature of the lowest sand and clay layer, rather than by the vacuum level.

It seems it wouldn’t hurt for the gravel pump to be a bit heavier, for example, by using a longer and heavy-walled tube, but this will also require more force to lift it up. Also the piston could be a bit heaver to sink more quickly, but well, you will figure out how to operate with the tool after a little while, and a shorter gravel pump is certainly more easily handled. Just make sure to wear proper work boots, because your toe may crack if you drop the gravel pump on it. An the serrated front will bite into your foot as nicely as it bites into hard sand.

As for the diameter, it seem that the 89 mm outer diameter is well suited for a DN115 well pipe. I could imagine that with a larger gravel pump, it may be difficult to withdraw, and will be overly heavy. So unless you gain other experience, any pipe around 90 mm outer diameter will work. I would suggest to use 88.9×5.6 which is a bit heavier, rather than the 88.9×3.6 used for the punscher. But probably all will work if you handle it right.

Down from the well: all kinds of sand

Most important for a well is the nature for the water-bearing layer. Already when using the soil drill I noticed coarse sand when hitting the water layer, and it is so liquid that it can be easily washed down and has almost no turbidity. This is basically a good finding, intermediately coarse sand, with little fines.

The top layer had a few larger stone, but in the water bearing layer, the largest were maybe about 8 mm in diameter.

Interestingly enough, the was a solid but -fortunately- thin layer of sand solidified by white matter in about 3 meter depth (just about 1 cm thick layer). Maybe the river running here over my land dried up some 1000s of year ago?

To color of the sand is somewhat red, but this color doesn’t wash out. Diffing further, from about 6 meters down, gray to black sand appeared. This sand was considerably finer and pretty difficult to remove by plunsching, so I used plenty of water and many strokes of a gravel pump to remove it (I modified the plunscher to a gravel pump by adding a piston – will be described in another post).

Finally, at about 7.5 m down, the sand turned more and more black with some brownish clay fragments and plenty of mica (shiny particles).

Given the 0.3 mm slot width of the filter, about 1-2 mm sand would be quite ideal as a water bearing layer, so I was definitely happy to hit solid clay about 7.6 meters down, and sunk the lowest pipe some 10 cm into this clay layer. Note that the clay layer is really heavy pliable clay, it doesn’t seem to swell or dissolve in water easily. So I even decided not to further close the bottom of the well pipe, it seems soundly stuck and closed by the natural clay.

Some study of the sand revealed that the 7 meter sand has quite some sharp and irregular particles that can clog the filter, so better to keep the filter out of this area as much as possible. Maybe the lowest filter section (2 m in total) is now in the black sand layer for about 0.5 meters.

7 meter sand:

Even more important in such case to not overload the filter, to keep sand from getting into the well by keeping the inlet velocity at well below 0.03 m/s, better 0.02 m/s, which is possible by taking about 2000 L/h through the 2 meters of filter section.

The sand in the main water bearing layer is looking much better, it is coarser, and has more rounded shape.

Red marked are some small gravel, and the red lines show millimeter distances.

Main water bearing sand at about 5 meters, microscopic picture:

For thoroughly removing all sand from the well, I used a sand sucker construction from regular PE pipe (32 mm outer diameter), and a 8 mm pneumatic hose inserted such that it is pointing upwards, and extending about 15 cm inside of the pipe. With ample supply of pressurized air (from a compressor) connected, it will pump up a mixture of water and sand even to 8 meters, no problem. Sure it is a mess of water, sand and dirt, but it is an easy way to get rid of all the fine sand and mica that can’t be effectively removed by the gravel pump finally.

I also supplied plenty of water by a flushing tool, finally, also used this to soften the clay and to flush out a few cm of clay, but introducing a fairly high pressure (6 bars) water jet and pumping out the dirty water at the same time.

I continued to pump out water with the air-operated pump for about 1 hour, finally, I connected an old electric pump to the well for about 3 hour, and during all that time there was basically clean water after the first 30 minutes. And so far it doesn’t show any sand residues after one week of use, so maybe we are safe. Let’s check in one year! Surely I will keep all the tools so I can flush out any sand or residues in coming years should need be.

Drilling and digging: a new well

Since I have moved to my new house, there are extensive gardens that need plenty of watering these days. So far, I have been using a 1984 driven (abyssinian) well, merely a 1-1/4″ steel pipe rammed into the ground. This well has been struggling to provide enough water, less than 500 L per hour. Probably it has reached the end of its life and all attempts to rejuvenate it helped for a while, but I have been looking for a more permanent solution.

That’s the old well – now closed with a cap!

Rather than building again a driven well, which is not quite suitable for the quantities of water that I am looking for, say, 2000-3000 L/h rate, I decided to try a drilled (open) well. Size DN115, which is 125 mm outer diameter, 5 mm wall pipe, specially designed for wells (GWE well pipe, PVC-U, K-series).

The first 80 cm were easily dug with a spade, it is mostly sandy soil with some gravel stones.

Further, I needed to use a soil drill. A neighbor provided it generously, and with some old pipes extensions were made to reach to about 6 meters.

The soil here in the Rhine valley is quite suitable for these kind of drills, in just two hours or so, and with plenty of sweat, the whole reached down to the water table at around 4 meters. Still removing some sand, but you can’t drill into a mixture of water and sand… it will just form a cavity.

There are other kinds of drill, but this is a close-up, a large corkscrew.

Before we proceed, we need to insert the pipe, now assembled to 4.8 meters: 0.8 m sump, 2 meter filter pipe (0.3 mm inlets), 2 meters of plain pipe. It is not all that heavy and I managed to get it in quite easily.

Now, we can already see almost to the center of the earth, at least, 4 m closer to the center…

The pipe needs to be securely mounted so that it can’t move around too much.

Next, we have to deepen the well by a process called plunsching. Bit by bit removing the sand from the inside, and lifting it up with the device, which is basically a steel pipe with a valve at the bottom.

It worked well with coarse sand, but with finer sand, I needed to tighten up the seal and modified it a bit to close tightly. Otherwise the fine sand tends to run out.

Also needed to make a special tool to reach to the screw at the bottom. All a bit inconvenient, but it works.

Also critical is the loading of the pipe, first, I added about 150 kg, later about 240 kg. Easily managed by some old concrete pavers that are about 10 kg each.

The plunscher, I attached it with 3 chain links to the rope, this held it better in place and it could be handled easily.

With up to 350 kg, (the load an my own body weight from time to time), we are well in the save area of the weakest link, the filter pipe.

According to the manufacturer, 2 meters of the filter pipe used should be good enough for nearly 4000 L/h, I may take 2000~2500 L/h, so there is a good safety margin

It is critical to stay below about 0.03 m/s water inlet speed, otherwise there may be effects detrimental to the lifetime of the well.

The cuts in the filter pipe are pretty precise, hard to do this at home.

After about 6.5 meters, things got really difficult, with fine sand, which was also pretty much solidified. I used various tools including water hoses and a mud sucker (a pipe with a PU hose inserted, pointing upwards inside the pipe). The mud sucker uses compressed air (I just supplied the full amount my compressor can generate) and at the top a mixture of sand and water will come up. It is a little mess, but convenient to operate. Also I added plenty of water to the well to keep the level as high as possible, otherwise further sand may be sucked in.

Finally, I reached a layer of clay, and with the help of large quantities of water and air, I managed to dig some 20 cm into it, but it seems really solid and pliable clay.

This scheme shows the well as sunk. it is about half-filled with water, and the suction point is located between the two filters, in an area of no inlets. Ideally, the inlet should be above the filter pipe, but I wanted to allow at least 2 m of water column above the inlet, and with the pump outside the well, the turbulences and local load on the filter pipe will be minimal.

The inlet is just a section of pipe, with many holes drilled into it.

The distribution system and piping as mostly done with 32 mm cold-water PE 100 pipe, connected to legacy 3/4″ piping of my workshop and garden, and some newer pipe (16×2 Pipetec composite pipe).

After only just a few minutes with an old pump to remove dirty water, already the water became nice and clear. Maybe because of the thorough work with the sand pump, there was not much dirt to remove. Also I decided against closing the bottom of the pipe, which now seems to be very solidly embedded in clay anyway.

The water is pouring out plentifully, it is pleasure to the eye and a delight forever!

Everything else could be done easily, just mounting a few pipes and machining a lid from 30 mm PVC plate.

Finally, protected it with some concrete plate and stones while providing easy access for removing water from the pipework in winter, basically, just opening the check valve at the top.

Etalon 77.19000 Height Gauge: a broken pinion

Recently, I found a nice offer on Ebay, an Etalon 77.19000 height gauge, along with a ultra high resolution Mahr LVDT length sensor. About the sensor, we will hear later, but the height gauge, although sold as “working”, didn’t work.

Still in good mechanical shape, and all Swiss Made. Mitutoyo has a very similar model, 192-130, which sells for well over 600 EUR.

The mechanism uses a rack and pinion design, with two pinions, one tensioned by a spiral spring, to avoid backlash. Practically, even without the spring – which was bent – there is no noticeable backlash.

There is also a second rack, and this drivers a fully independent counter mechanism.

After some examination it became clear that one of the pinions had a broken shaft, and this also let to the other pinion spring being damaged. The spring was easily fixed, but the broken shaft of such a tiny and hardened pinion, hard to fixed. I managed to drill a hole with a carbide drill, but when pressing in a new shaft, the whole thing broke apart…. a disaster.

Looking around in my drawers, I would this cheap Chinese dial, 0.01 reading. What if it uses the same rack pitch? Indeed, it does. The dimensions seems to correspond to a module 0.2 gear, and examination under the microscope showed identical tooth count on the pinion. Only the drive gear is a bit different but this could be pushed off.

The gutted dial, well, it is less than 10 USD.

To assembly it, I cut off and ground the lower part of the old pinion to a diameter a little bit less than needed, made a sleeve from stainless steel, and ground a suitable cylindrical length of the spare pinion so that all can be pushed together and fixed in the sleeve to form a new gear assembly of the correct dimensions.

All quickly done with a tool grinder and a lathe. And with the new gear, the Etalon is good as new!

Workshop Upgrade: Laser cutter and engraver SCULPFUN S9

There are various laser engravers or cutters available in the market, so it is hard to make a choice. Finally I got a Sculpfun S9, which appears to be well-regarded in the community as a cost-effective and capable machine. I was also looking for something that is easily serviceable, not using custom controls or special motors – the Sculpfun S9 is built from all relatively standard components so it can have a very long service life even if I eventually need to fix the electronics or replace the controls altogether.

The machine ships as a kit, but there are good instructions for assembly, step-by-step, even the screws packaged for each step in a separate bag.

The machine is fairly portable, so you can also set it on the surface of large panels to do local engraving or similar.

Some first tests, works very well indeed! Just the smell of burned wood and plastic – it is really not a machine for an apartment, and the laser also seems no toy for kids. It is fairly strong and can be dangerous. This laser has a very sharp (maybe 0.1~0.2 mm beam) that cuts through several mm material in a single cut. No good idea to get your fingers in the way.

You can also cut foil. Maybe better to use a knife cutter (because of the smell and vapors), but for some once-off jobs, it is easy to use and also cuts uneven old foil very well in my test. Better use some magnets to push the foil down on a piece of sheet metal.

The main application that I am looking for is to cut custom seals from plain seal stock. The machine cuts well through 1 mm Elring Abil plate, and similar materials. Even thin rings can be cut, no problem (very hard to cut with a cutter knife or punch).

Next step will be to get the machine properly installed. This means, adding an air nozzle to assist with cutting (made from brass), a machine table, and an enclosure with exhaust fan to get rid of the toxic vapors.

The nozzle is made from a piece of brass (several of these pieces purchased at a scrap yard 25 years ago when I was still a kid).

The nozzle has a side inlet, and is designed for about 20 L/min with 1.5 mm diameter, so we are looking at 150~250 m/s linear velocity at the nozzle outlet.

The gas is fed through a 4 mm PU pneumatic tube.

To measure the air flow, we are using a very cheap Chinese gas flow meter. This has a needle valve, but it is not working well – the needle valve puts a spin on the gas, and the indication is incorrect (the sphere starts oscillating and spinning), so I use a separate needle valve (FESTO GR-QS-8) in the supply pipe.

The flow meters comes with flimsy plastic connectors, and these have 5/16″ UNF (24 TPI) tread… not a very common part in Germany to get a transition from 8 mm pneumatic tubing to 5/16″ UNF…

Fortunately, found a suitable thread cutter in my tool selection, so an adapter was made quite easily (from 5/15″ UNF to 1/4″ NPT, then us a 1/4″ NPT to 8 mm push-in tube connector).

The next step has been to make a suitable table, sure you can put the laser machine on some ordinary table, but it has quite some speed and movement and even relatively stable tables will be moving and there is some impairment of precision. So I wanted to give this machine a stable basis that doesn’t shape. It is all welded construction from about 1.5″ square steel pipe. The top is 18 mm waterproof plywood. There will be a piece of zinc-plated sheet metal on top, also to use magnets, and a open cutter support plate on top in case of heavy cuts.

To fabricate such a table, after the welding is done, grind off the scale (this is just plain steel), clean with acetone, and then roll-on some primer paint.

Finally, painted in a blue-gray color, and with the top plate mounted.

Next step, fabrication of an enclosure with a movable cover. All made from 15×15 mm (about 3/4″) square tube, all TIG welded…. looks easier as it is with all the parts and angles.

There will be two large windows, 40×60 cm, to observe the process. I selected GS-1C33-GT Plexiglas (acrylic glas) which is nicely transparent for visible light, but blue light of the laser can’t pass at all.

This is also confirmed by the spectrum, the laser is emitting at about 452 nm.

After some hours of work, the enclosure is ready for painting. It opens nicely and smoothly, also because of a gas spring (200 N, 535 mm total length, 220 mm travel).

It is one of the few occasions that I have use gas loaded springs in my design but it is working well. Just the design calculation is complicated and probably it is always a bit of experimentation to find the right gas spring size and force. But this time, successful at the first attempt. My recommendation, to rather use a slightly stronger spring (say, 200 N if 150 N is calculated) to allow for aging of the spring or other design uncertainties.

Workshop Upgrade: 3D Printer

Finally, I had to opportunity to acquire a long desired tool, a 3D printer. In recent years these have become fairly affordable, and also easy to use. So it is on longer needed to spend days with optimizing various settings. I am planning to print mostly in durable parts, so I am targeting PETG and ABS rather than PLA plastic materials. Mostly planning to use it for spare parts, or mold patters for aluminum casting.

The machine, it is an Artillery Sidewinder X2, a great product, all nicely arranged in a box.

It didn’t take long to set it up, maybe one hour, and then you can use the well known software packages to run the machine. I am using Freecad for modeling and Cura for processing.

All worked fine already for the first part… great!

A cylinder, and a space shuttle. All fairly robust.

So far, I can only praise the machine, it is working fast and precisely. Just printing low cost PETG material. Key point is to keep the bed rather hot to keep the parts sticking, and then just remove them after cool-down with no effort.

SMEG CS19ID-6 Range: another defect

It seems my SMEG kitchen range is getting older… at least it is again showing some issues. The right hand side front induction field is sometimes coming on, intermittently, only to shut off quickly again. Normal operation is no problem, but when it is switched off, it doesn’t remain fully switched off all the time. Could be dangerous if some pot is left on the induction field, and the range decides to switch it on by itself… a praise to all the old-fashioned switches that completely took power off the appliance.

First we need to find out the source of the issue, is the it controls electronics, or the switch? To test, I opened up the front panel (easy enough, it is just 8 screws…), and switched the cables going to two of the front panel switches. And, as it turns out, the issue also switched. So it is probably a defective switch rather than any issue with the electronics. That’s good news.

For about 35 EUR, I got a new switch, as it turns out, it is no switch put a potentiometer…

… and a quick exchange fixed the issue. Now let’s do some study of the old part.

Made by printing some conductive composite on a circuit board. Looking good. I can’t see any issue with it even under the microscope. Maybe just some contact issue, the contacts also don’t look clean.

So I will clean it all up thoroughly, bent the contacts a bit to give it slightly more force, and keep it as a spare.

These potentiometers aren’t cheap, at least the use good engineering plastics for it, like, glass fiber reinforced materials.

A Japanese hot pot: A hot spring without a hot spring

One of the most famous features of Japan is the availability of hot spring all around the country. If this is an advantage or disadvantage of my new living place in Germany remains yet to be seen, because the hot water close to the surface normally comes along with other earth activity including volcanos and earthquakes… Anyway, I have no source of hot water here other than by gas heating, so at least I wanted to have an outdoor bath resembling Japanese style.

The pot is handmade from high alumina clay, fired at about 1350°C, and shipped from famous Jingdezhen, Jiangxi China, within about 8 weeks. It is a heavy pot, about 350 kg. It resembles the Japanese made bath pots 1:1 but the price is much more competitive and a certain Ms. Wei of the pot company knows how to deal with foreign customers and can manage export of such items as a routine business… Transportation fees in Germany and customs duties, taxes turned out to be more costly than the pot itself.

The essential elements are, (1) the pot, (2) the piping system all made from DN40 glue-fitting PVC-U pipe, (3) a circulation pump (180 Watts, Wiltec 51554, including a filter/strainer), (4) a gas heater (fired by Propan), (5) hot water supply pipe – this is constructed such that it can be drained easily in winter after each use, so it is possible to have a bath also in freezing conditions, made from 18 mm copper pipe and fed by the main hot water system of the house (using natural gas), (6) a regulator system to keep stable temperature.

The water heater has a safety system to switch off the heater after 20 minutes of use, and it has a built-in electric ignition system powered by 2 batteries, 1.5 Volts each. In order to achieve temperature regulation without interfering with the internal circuit of the gas heater, I just switch on and off the 3 V power to the heater.

Normally the heater is only used to keep the water at constant temperature of about 42°C (Japanese baths are really hot…), which takes less than 20 min on-time, anyway, I decided to add a timer circuit that interrupts the heater ever 15 minutes for 30 seconds. So essentially, it can continuously heat the bath even when filling in cold water. Normally the bath is started with reasonably hot water from the house main supply.

Unfortunately, the ignition system by high voltage causes the regulator to hang up. The high voltage sparks change the ground potential it seems, and even some attempts with protection and clean-up circuits (low pass filters) had no permanent effect, when powered from a single supply that is split to 12 V the regulator/timer, and 3 V for the heater. So I now powder the unit from two completely separate powder adapters, and two completely separated circuits, isolated by mechanical relay.

The voltage regulator for 3 V is a simple LM317 circuit, with some more capacitors and features to protect it from any surge voltages.

The temperature regulator and timer, sure you could build it yourself with some microcontroller, display, etc, but no need as the complete module is available for less than 3 EUR mail-order.

The water circuit has the circulation pump. Note that not all the water is passing through the heat, only a certain portion, and pressure is generated by an orifice in parallel with the heater. Temperature sensing is done in the circulation loop. In winter the circulation system can be completely drained and switched-off by appropriate ball valves. So you can still have a bath, but you just can’t heat it by the circulation system (rather need to add more hot water, or just limit the bath to 1 hour or so).

The heat loss seems to be about 1 kW, so we need to run the heater that is using about 1.2-1.4 kg of propane per hour of operation only for some minutes at a time (1 kg propane has about 14 kWh of energy, and we may assume an efficiency of 0.7). Experience shows that is this correct, the heater may switch on every 15-20 minutes of so for about 3 minutes.

Now the system is completely automatic. In normal usage there is no need to adjust any regulators. Just fill in water and switch the bath main switch to “ON”.

Lastly, the water is not just plain tap water but sure enough I am adding bath salts composed such that they resemble my favorite Yamaguchi prefecture hot spring pretty well!

Heating energy consumption: first evaluations, and total annual energy demand

In the meantime, I have collected enough consumption data for gas consumption (mostly heating, some little bits for hot water), and at various temperatures outdoors, including, very cold temperatures.

As it turns out, the gas consumption correlates well with the outside temperature (daily average temperature in 2 m height, as officially recorded close to my place by the weather authorities).

With datasets of daily temperatures for 2019 and 2020, we can then estimate the total gas consumption of these years.

The 2019 predicted consumption:

The 2020 predicted consumption:

For German standards, everything less than 100 kWh per m2 and year is quite reasonable. I need to admit that not all of the rooms are fully heated all the time, but well, it is not all that bad, comfortable, and affordable.

Here an energy rating chart – in German – around 100 is a good value, above 200 … there it is getting really bad, wasteful and expensive!

Christmas Time: Honigkuchen (honey based cookies)

It is a long time favorite, and easily stores for some months – honey based cookies. Here is a good recipe.

500 g Honey
125 g Sugar
150 g Water (you may just add some more Honey if you don’t like to add refined sugar, but it makes the dough easier workable)
1 kg wheat flour (can be some coarser type wheat flour)
60-80 g Spice including anise, clove etc., a ready purchased mixture. Adjust quantity to strength of spice and your taste
25 g Ammoniumbicarbonate (“Hirschhornsalz”)
Pottash can also be added, by I didn’t add it, it will make the cookies flat.

First, mix and melt honey, water, sugar, at low heat. Add the other ingredients and work firmly. Let it rest for 2 or 3 days in the fridge (cover to avoid drying out).

Then, prepare cookies, and bake at about 200 degC for 8-10 minutes. These need to be well baked. Underside can be dark brown, but don’t burn them to bitterness.

The Honigkuchen can be stored in a well-closed container for 2 or 3 months no problem.