Explosive Enterprises
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Adjusting GBB Rocket Valves
🕑 Added 2025-08-23 18:21:36 +0000 UTCWe've covered this in a couple of videos, but now that we can make Patreon posts that are way easier to reference than a video timestamp, it's time we document rocket valve modification for power adjustment.
This modification applies to TM-style and VFC-style rocket valves, and there are two reasons to perform it:
You have a fixed rocket valve and need to adjust power to get it under field limits.
You have an adjustable rocket valve but find it's inconsistent when reduced to under field limits.
In either case, this modification will reduce the amount of gas going through the rocket valve. For a fixed valve, this will simply reduce power. For an adjustable valve, this will shift the entire adjustment range of the valve downwards. Since adjustable valves typically become less consistent the lower they are adjusted, this will allow you to 'open up' the valve a bit to achieve the same power as before while making it more consistent.
You'll need:
-Your rocket valve (we'll be using a VFC-style adjustable one)
-5mm OD, 4mm ID styrene tubing
-(Optional) 4mm OD, 3mm ID styrene tubing if further reduction is needed
-Superglue
-A knife suitable for cutting styrene
First, take your 5mm OD, 4mm ID styrene tubing and smear superglue around the end:
Now insert it into the front of the rocket valve until it just reaches the window:
Give that time to dry, then cut the styrene flush with the front of the rocket valve:
At this point, if you only needed a slight reduction in power, you're done. But if you need more, then the 4mm OD, 3mm ID tubing comes into play. Repeat the above process with the smaller diameter:
This process can be repeated as many times as needed, but we haven't yet encountered a replica that needed smaller than this- reducing the inner diameter of the rocket valve from 5mm to 3mm already achieves a roughly two-thirds reduction in cross-sectional area.
If this has gone too low and you need to increase power again, it's easy to fix. Simply wait for the glue to fully dry, then use a drill bit to bore it back out as needed:
In this manner you can fine-tune the power of a fixed valve by shimming it to the nearest millimeter, then boring it back out to the desired final diameter.
For VFC-style adjustable valves, however, we have found that a 3.5mm inner diameter produces stable power from 0.9J-1.6J using .32g BBs in most replicas (at room temperature). Some may benefit from slightly narrower, others slightly wider, and ambient temperature will affect power as well, but this is a good starting point.
Thanks for reading, and we hope you find this useful.
Comments
Nomis
It worked perfectly to make the northeast Famas playable on my field with a 1.5 J limit. thanks ❤️
Ross Radford
This set contains all the appropriate sizes in essentially lifetime supply: https://www.amazon.com/dp/B09Z2K52P4
Justin Dyer
One thing I'd like to know is within the US, what are good places to source the tubing from. I ordered some 5mm OD 4mm id tubing from eBay and received some that were closer to 5.5 OD and 3.5 ID
VFCeemoreButts
Cheers guys, loving this short form written style content.
