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Alstone · Moderator & Site Supporter

The Rohm Twinmaster Co2 in its basic form outputs about 2ft/lb or 360ft/sec and a lot of people have asked how to increase the power of these guns, but the whole subject concerning power increase of Twinmasters seems to be shrouded in mystery, either people say it is to difficult to attempt but won’t say what the job is, or someone wants to charge you £50.00 to do the job.
So this is my solution to increasing Twinmaster power, it very easy and reversible.

To get more power you need to increase the amount of gas behind the pellet and to do this the gas valve needs to be opened for a longer time, with the Twinmaster the gas valve is opened by the hammer hitting the valve stem and lifting it off its seal, now the valve is held shut by first a spring and second gas pressure, when the hammer hits the valve stem it pushes the valve away from its seal and lets gas flow through to the pellet, then the spring pushes the valve shut and lifts the hammer back to its start position, if you could prolong this open period more gas would be let out and increase the power of the gun, and all the spring does is close the valve so if we weaken the spring by a small amount it will increase the valve open time and increase the amount of gas let out, this can improve the output of the Twinmaster up to 4.ft/lb or 500ft/sec.

When doing this the adjustments are very small, as supplied the valve spring is approximately 0.372” long this needs to be shortened by 0.24” to 0.348. to do this bend the coils down by a small amount “DO NOT CUT” and check with a vernier gauge or micrometer. After refitting the valve make sure that it pushes the hammer back without any hesitation, if it does not, lengthen the spring by a small amount until it does.
This may look a bit complicated but in actual fact it is very easy, just take your time, don’t bent the spring to much at once just in small stages, and when refitting smear some oil on the large Green O-ring and the valve stem. If it all goes wrong bend the spring back to what it was when you started. Have fun!

AL

AirGunEric · Site Admin

Nice that the Twinmaster actually has metal parts- i.e. the valve- unlike many modern Co2 guns with plastic valves. With a steel piece as that appears- have you ever tried machining it out to give it more volume as well?

And- what did the spring change gain you ultimately?

Alstone · Moderator & Site Supporter

Hi Eric
I did think about increasing the expansion chamber which runs down the side of the valve chest, but it would have made the wall thickness a bit on the thin side,
The increase has been in the region of 100ft/sec which is about 25%, it is possible to push it a bit more but I am quite happy with the results.

AL

AirGunEric · Site Admin

I hear what you're saying about the wall thickness- which is one of the reasons I'm not a fan of newer plastic valves- even less potential for improving them.

What size (diameter) is the spring on this valve? I.e. is it a simple to find replacement, or is the only real option shortening the stock unit?

Alstone · Moderator & Site Supporter

Hi Eric nice to see you back.
I think I was talking at cross purposes reguarding the vavle unit, I was thinking of increasing the expansion chamber. Anyway back to the subject of the valve, it is made of very hard steel and ported to the maximum, the only thing you can do is smooth of some of the angles to give a better flow to the gas, this I think would give a little improvement in power but the porting is very close to the valve seal ring and one slip with the grinder and it all goes down the drain. One thing I have found out is that the type of lubricant used in the valve makes a diffrence to the power output by up to 20ft/sec, it works best using a very expensive Synthetic oil but this does not last for the full Co2 capsul it gets washed off before the capsul is empty, and as this is inserted through the capsul pieceing pin it is not possible to replenish it during the life of the capsul, so I use agood quality silicon oil which keeps the valve lubricated for a full capsul. Some of these claims that capsul's contain a lubricant I think have to be taken with a pinch of salt, I have removed the valve after using some of these and found it to be as dry as old boots, so now I use a cheap bulk buy general purpose capsul and introduce the lubricant myself.

As for the spring the ID is 0.290 and OD 0.350 wire size is 21SWG, Which I think should be quite easy to obtain, also you do not need to shorten the spring by cutting it just squeeze it together with a pair of plier's and that should be enough to make a diffrence.

Just a thought while typing this, I don't know what it is like over there concerning Climate Change but over here the goverment seem to have gone mad about it, putting taxes on anything and everything and trying to ban anything that causes Co2, which brings me to the point, when will they ban Co2 capsul's, because as soon has some loony in goverment gets wind of the fact that we use it for our hobby they can kill to birds with one stone ?, air guning and Co2 use. anyway I just rambling again but it's food for thought.

AL

AirGunEric · Site Admin

Pollution/Environmental stuff is the big concern everywhere it seems- except of course the places that will be the biggest contributors to the problem in the near future- the Asia-Pacific region.

I think it would be tough to ban or tax Co2 used in airguns as a pollutant or "greenhouse gas" because no one is "creating" it- it is collected as a by-product of some other, primary purpose. I.e. it is collected from another process- I don't know specifically which/what process- but maybe something like being separated (in a gaseous state) from petroleum when it's pumped up from the bottom of the sea or sand. Maybe this won't matter- if any process/extraction method becomes more expensive because of the environmental concern- the costs tend to bleed into any/all products that come as a result of this process- so the fact that no one is "creating" the Co2 we use by combining, burning or otherwise altering another substance with the only purpose being to get the Co2- may be irrelevant. The bonus is, while the price may go up- I don't think it could be outright banned- it will still end up high in the sky anyways.

Hmm- was that understandable?