Reviews > Cook Gear > Stoves > Trekka or Gasmate gas stove > Owner Review by Roger Caffin

Owner Review - Trekka Gas Stove
Roger Caffin
24-July-2005

Product details:

Notes on the brand

I was given several of these 'Trekka' stoves by The Sitro Group many years ago for a product review of stoves I was writing for a local bushwalking magazine. Since then it would appear that The Sitro Group has changed the branding (from Trekka to Gasmate) and also slightly changed the design of the stoves. The new model numbers are GM1157 and GM1158/PL. Both old and new models were made in China, but apparently at different factories. The new models have about double the power rating of the ones reviewed here. However, I note that many local shops are still selling the old models, so the change may be recent.

Basic Product details:

This is a robust steel and brass stove for use with the industry-standard screw-on butane/propane gas cartridges with the B188 Lindal valve. It can be obtained as shown above, or with a fixed wind/radiation shield and/or with an added piezo igniter. The full kit is illustrated below. (The coloured pointers are explained below too.) I will go through the design in some detail as this stove really is a good example of the generic gas stove, and the basic principles given here apply to all gas stoves. The only extra item some stoves may have is a generator tube, such as on the Snow Peak GS-200D.

The basic stove has a solid brass base which screws onto the gas cartridge. On top of the base there is a shaped steel housing which supports four bent steel wire support legs. These legs are retained by non-removable circlips (not shown) pressed onto the bottom ends of the legs, and are free to rotate. This steel housing is held onto the base with a shaped flat nut. Above this there is a brass tube or central column leading up to the burner head, which seems to be a press-fit onto the brass tube. The brass tube screws onto the base above the flat nut.

The brass base houses the screw coupling for the standard 7/16" thread on the gas cartridges. There is a centre pin (purple line, pic 3) inside this which actives (opens) the Lindal valve. Above this inside the base there is the needle valve (pic 4) which controls the gas flow, and finally at the top there is the jet (blue line, pic 2, purple line, pic 4). The jet body contains a fine disk of stainless steel mesh pushed up inside it from below; this acts as a final filter to protect the fine jet hole. The needle valve has a very fine thread (yellow line, pic 4) and is sealed in place with double O-Rings (green line, pic 4). The point of the needle valve (red line, pic 4) is quite solid: it relies on the fine thread for sensitivity of control. This valve is held in place by a threaded bush (green line, pic 2; yellow line, pic 3, blue line, pic 4) as well. Finally, the coupling to the gas cartridge is sealed with two O-Rings: one inside the coupling (blue line, pic 3) and one outside (green line, pic 3). It is vital that these two O-Rings be in place and in good condition to avoid any chance of leaking gas.

The burner head sits on top of the central column, a brass tube some 40 mm (1.5") high and ~14 mm (1/2") in diameter. This column screws to the base. There are four holes (brown line, pic 2) in the column symmetrically arranged around it just above the top of the jet: it is through these holes that the air is dragged by the high velocity gas stream out of the jet. The gas is pre-mixed with the air as it swirls up the column and out through the burner disk. The burner disk is an interesting assembly consisting of two layers of pressed metal. The underside layer has a contour which closely matches that of the top, such that the gap between the two is quite small. The gas flows through this gap to emerge at the holes punched around the periphery of the top layer. The outer surface of this top layer is smooth, but it is clear that this is because the shaping was done after the holes were punched. The edges of the holes show signs of having had the rough edges severely flattened.

The four support legs are made of quite robust steel wire about 4 mm (0.16") diameter. They present a flat surface on top for pots and kettles, although the top edge of the wire has been roughened (yellow line, pic 2) to provide drag to prevent the pots from sliding around. Without such drag pots can even slide off the burner: I have seen this happen. The four legs can all be folded sideways if the windshield is not in place: this reduces the effective volume of the burner considerably, making for easier packing. The legs could in principle rotate to one side while the stove is running, heating a pot of water, if there was not some way of preventing this. In fact there is: the base of each leg has a crimp (purple line, pic 2) in it which can be aligned with a slot in the mounting hole in the steel housing. When the crimps are aligned with the slots, and the legs pressed down to push the crimps into the slots, the geometry is quite stable. Pulling the legs back up allow them to be rotated into the packing position.

Add-on Product details:

Shield

The windshield/radiation shield (red line, pic 5) can be added to the basic stove by unscrewing the top burner part from the base, placing the flat metal shield on top of the four support arms, then placing the burner tube down through the hole in the middle and screwing it back onto the base. When the burner is done up tight it holds the shield onto the support arms via four grooves in the shield. Note however that once the shield is installed, the suport arms can no longer be folded to one side: the packing volume becomes much larger.

There are three cut-outs (yellow line, pic 5) in the shield. They let a little radiation through to warm the gas cartridge underneath, and they also let the flame from a match or butane lighter come through to light the gas. There is no cutout in the fourth quadrant, over the control valve. This prevents the control valve from being overheated by radiation. Bypassing this, or allowing radiation down from outside this shield, can result in a melted control valve knob. This did happen once when I was doing a lot of toasting of muffins - ahem.

It is conventional to call the shield a 'windshield', but this is very much a misnomer. Most of the flame is above the rim of the shield, so adverse winds can affect the operation of the stove. The radiation-blocking function is, in my opinion, far more important. It prevents the stove from overheating the gas cartridge underneath - an eventuality which would be both alarming and extremely dangerous.

The windshield and the piezo-igniter (next item) are shown on a basic stove in the picture to the right. The white porcelain insulator can be seen above the rim of the windshield. The piezo-igniter wire has a large pointy object at its tip, and I haven't the faintest idea of why. But it works.

Piezo-igniter

This is a small add-on (green line, pic 5) which can be attached to the central column. It consists basically of a piezo crystal in a tube and a wire leading up to the top layer of the burner. When the push button (blue line, pic 5) is pressed a plunger strikes the piezo-crystal with a blow. This creates a momentary pulse of very high voltage which is allowed to arc from a pointy object (purple line, pic 5) at the tip of the wire to the burner face. This very hot arc ignites the air/gas mix coming out of the burner. Instant operation! Naturally, the wire has to be insulated between the piezo crystal and the tip: this is done with a sleeve of white porcelain seen just above the rim of the shield in pic 5.

The inclusion of a piezo-igniter is not without some problems. They can be a little delicate, depending on the model. The igniter provided with one of these stoves lost the push-button during shipping. Without this it didn't work of course: most frustrating. The supplier simply replaced the whole stove.

Case

A rectangular black plastic case was provided with the stove. It weighs 166 gm (5.8 oz): more than some complete stove packages! It is extremely strong, and in practice just getting the lid off can be a major wrestling match. The case is just slightly larger than the stove, such that the stove fits neatly inside. However, since the steel stove is so very robust I do not bother with the case.

Field information

As mentioned at the start, I was given a few of these stoves while writing a stove review for a walking magazine. It is unlikely that I would have thought to buy any of them as they are so heavy. However, since they are so robust I decided to use them for cups of tea and coffee on day walks, since weight didn't matter much. One of these stoves has been thrown into the top of my pack (and 'thrown' is not far wrong either) most every weekend for the last six years. The stove has continued to function with complete reliability. It can be turned up to boil fairly quickly, yet it can be turned down to a very low simmer. The shield works quite well in protecting the gas cartridge under normal use. The two external O-rings have stayed in place and not deteriorated at all over the years.

The only routine maintenance I have ever done to these stoves has been to lubricate the various O-rings with a very small amount of silicone grease. That's the two external O-rings on the gas seal, plus the two small O-rings on the spindle. Well, I think I added a touch of silicone grease to the thread on the valve spindle as well. This has been done maybe once every couple of years. All this sounds very good, but the good performance was not achieved without some initial modifications.

Modifications

The early performance was not satisfactory: the burner seemed to heat water very slowly. The manufacturer claimed a power output of 5,600 BTU/hr (1.64 kW), which is small compared to my Snow Peak at 10,000 BTU/hr (2.93 kW), while the burner area was far larger. Opening up the valve to try to get even this amount of power seemed to risk 'flame lift-off', a very serious hazard. This phenomenon is poorly illustrated in picture 6. It will be seen that the flames are well connected to the burner at the left side, but appear to be floating above or away from the burner on the right side. It is due to excessive gas velocity at the burner face, exceeding the flame velocity of the air/gas mix. Under more extreme conditions part of the gas flow can intermittently cease burning.

I decided to take a closer look at this problem. I found that the holes in the face of the burner were partly blocked: the rough edges of each hole had been burnished over, as mentioned above, reducing the size of the openings. This is visible in picture 7 in frame A as bright rings around each hole. I thought this reduction in hole size might be a reason for both the poor performance and the threat of flame lift-off, so I dismantled the stove and drilled out every one of those holes in the top two rows. The amount I increased the hole size may be seen by comparing the amount of metal between the holes in frames B (undrilled) and C (drilled). I also added an extra row of small holes at the bottom of the face, below the pre-existing third row. All this improved performance significantly and eliminated the lift-off hazard. Tea and coffee were ready much sooner: a nice thought. However, I must emphasize here that doing such a thing invariably voids any warrantee, and it should not be attempted by anyone without a detailed knowledge and understanding of how these stoves work.

I have also successfully 'hotted up' another one of these burners considerably more than this, to about double the original power rating, to exploit the large burner area and just to see if it could be done. (The same caveat applies of course.) I mention this here to emphasize that the basic design of this stove is good. The newer versions appear to have had similar changes as they now claim double the old power ratings.

I will add here my own opinion about the 'manufacturing quality' of the stove. The basic design is very good, but I have no idea where this design work was done. The machining is fairly good too, except for the burner face and holes. Here I see some familiar problems with Chinese manufacturing: there does not seem to have been any quality control feedback to the factory once the design went into production. The problem with the too-small holes was not picked up and remedied in these models. This is a pity.

Servicing

There is little to go wrong with this stove. A single nut on the valve spindle (green line, pic 2; yellow line, pic 3) can be undone to allow the spindle to be screwed out for cleaning and greasing. The thread is fine: do this carefully. The burner unscrews from the base, and removing the nut on the column allows the steel housing to be removed. The jet (Blue line, pic 2) can be removed from the base for cleaning. Tools for all these operations are not supplied, but I doubt many would ever need to do either of these jobs in the field. I do service my stoves at home, but I find it is the liquid fuel stoves which need it, not the gas stoves.

While the disassembly of the stove sounds simple, such is not always really the case. The flat nut is shaped to accommodate the root of the thread: this means it must be replaced right way up or the steel housing will be left loose. The removal of the burner is simple when the piezo-igniter is not present, but it is quite a bit more tricky when the lumpy tip on the end of the wire overhangs the burner face. There is room, but only if I move the burner and the windshield sideways to exactly the right position. If I want to remove the shield when the piezo-igniter is installed I must first remove the burner and then rotate some of the support legs to the right position before I can get the shield away from the igniter. Everything is possible, but (Chinese) patience is needed! I should add that the only times I have needed to disassemble these stoves were once when I was drilling out the holes in the burner and the other time when I was arranging the bits for the photos shown here.

Footnote re gas behaviour in the cold

Butane boils at -0.5 C (31 F), while propane boils at -40 C (-40 F). On a very cold day - say around -10 C (14 F), the propane can still boil but the butane will sit there doing almost nothing. Carried too far, the propane gets all used up and the cartridge is left with lots of butane but not giving out any gas. This is why some people think gas stoves don't work in the snow: they simply haven't managed their stove properly. The radiation shield on this stove does screen the cartridge quite well, so I do not use this stove in really cold weather.

Summary

Would I buy another? I might be tempted to do so for day walks, but not for extended walks. The need to drill out all the holes to get the stove performing the way it was probably designed to work (and the way I want it to work) was a negative. I might try one of the newer versions, or I might simply try another cheapish brand.

Biographical information

Backpacking Background

I started bushwalking (the Australian term) at 14, then took up rock climbing at University with the girl who became my wife and is my walking partner. Later on we took up ski touring and canyoning. Winter and summer, we prefer long hard trips by ourselves: about a week in Australia, up to two months in Europe/UK. We prefer fast and light in unfrequented trackless country. We would be out for at least three months a year. Over the last four years we have reduced our pack weights for extended walks from 18 - 20 kg (40 - 45 lb) each to about 12 kg (26 lb), including food. I designed and made much of our lightweight gear myself.

I am also the maintainer of the Australian aus.bushwalking FAQ web site www.bushwalking.org.au/FAQ/.

Reviews > Cook Gear > Stoves > Trekka or Gasmate gas stove > Owner Review by Roger Caffin