CPH help please

[the oncoming storm]

I have been Thinking about building a CPH and although sscenteral tells you how to build a pump and separait PC firing system, I want to build CPS bladder. I assume balloons with a clip to keep it from moving will work but i don't know

[atvan]

Have you read JLSpaceMarine's article about his custom assault rifle? It is in the homemades section, and there is a nice big picture and linky on the front page. It details how to make a spherical bladder out of balloons. You could also get some ideas from reading some of the archived threads there about k-mods, because there are some great tips. The search feature will work wonders if you want to look through old threads.

The reason that spherical bladders are rarely made for CPHs is that it is a pain to layer all the balloons, it contributes to an awkwardly tall and wide blaster, and LRT is fairly readily availible in several thicknesses and sizes for layering.



Also, you only really need to post a thread once.

[martianshark]

It actually doesn't say much about building a balloon PC. Latex rubber tubing would be easier if you want to buy it.

Have you built an APH yet? I would recommend building an APH before trying to build a CPH. If you build it in a certain way, you could even convert it to CPS later.

You could also build a hose-charged CPS. That would be easier.

[mr. dude]

I've tried both, LRT is so much easier to work with. It is harder to get a hold of and balloons aren't too challenging, they just take a lot more time (and maintenance).

Now, I've never used this stuff, but you can find it at any hardware store, it's a balloon that unclogs drains through water pressure. I'm not sure what kind of performance it can generate, but it could be a better alternative to the hours of work party balloons will require.
Here's a picture:

[martianshark]

That's a cool idea. I did some searching and found something similar with less dead space. http://www.amazon.com/Cobra-Products-33 ... B000KKRQUM

[mr. dude]

Yup, you can find them in a variety of shapes and sizes at basically any hardware store. They just require a quick sealing of the hole at the other end. Again, I have no clue what kind of performance it'll yield, but believe me, only use balloons as a last resort.

[Andrew]

Apparently they run at 10psi operating pressure, but that doesn't seem enough even to clear a drain to me??

There are rumours quoting 50psi on some DIY/Hardware forums, but nothing solid to back this up. Shame really.

The LRT is probably the best option, it's easier to use and makes for a homemade with better performance.

only use balloons as a last resort

They tear easily, never seal properly. nuff said.

Instructions for LRT CPH (SuperCPS)

Instructions for Balloon CPH, in-case, for some reason, you use balloons instead (CAR)

[the oncoming storm]

Thanks guys but can you tell me how to close off the ofther end of a LRT just using a hose clamp seems flimsy.

[atvan]

Put is a short bolt and use the hose clamp on that.

[mr. dude]

Hose clamp isn't flimsy at all, it's what holds the LRT onto the rest of the CPH.
There's what atvan suggested, I use a hose barb/endcap and put a hose clamp on that, as long as you find something that seals it well.

[atvan]

I think he meant just a hose clamp onto the LRT with nothing in the middle. That would definately not work.

[Andrew]

+1 for the bolt.

Pic from SuperCPS guide (bottom left):



Use some kind of PVC or DUCT tape under the hose clamp to stop it cutting into the LRT. You shouldn't need teflon tape to seal between the bolt and the LRT as long as the hose clamp is tight enough. Besides, a layer of PTFE tape might make the bolt less secure (reduces friction between LRT and bolt). After all a form of teflon coating is used in non-stick pans!

On another note, has anyone tried putting the bolt in the other way round??? If the large hexagon bit is inside the LRT, and the hose clamp is tightened down onto the threads, there is no chance of it flying out of the tubing. (again!)

And as long as any sharp edges are filed down, it wont damage the inside of the LRT either!

[martianshark]

I don't think that would be a good idea.

[Andrew]

As long as the hexagon bolt head isn't too mugh larger than the shank of the bolt (a couple of mm, maybe less? Just enough to hold it in place but not enough to bulge the LRT too much anyway.), then the only difference is a bit of added security. Surely no-one wants to see another XP Backfire???

Filing the hexagon head down into a sort of sqaushed sphere shape would put even less strain on the LRT.

[mr. dude]

No need for the extra security, anything+hose clamp will hold very securely.

[Andrew]

No harm in extra security if there is no apparent downside, but I suppose I may just be being paranoid.

To be fair, a good PC case will contain any failures, and a ruptured bladder is more likely than a flying bolt!

[martianshark]

I would just do it the normal way. The head might push into the inside of the tubing and damage it.

[the oncoming storm]

Okay thanks for that here is another question. how long does the PC need to be to hold 20oz. (the plan is to build a CPS 1200 replacment I don't trust it to last. the crack is back)

[wetmonkey442]

Volume can be calculated using the formula L*Pi*R^2 = V, where L is the length of your PC and R is the radius (ie half of the inside diameter of the pipe).

Basically just plug in whatever diameter pipe you want to use into that formula, set it equal to volume (convert 20 oz to whatever unit of measurement you used for diameter, cubic inches or cubic centimeters), and solve for L. L will be the length in whatever unit you used.

[atvan]

I recommend converting to metric too- everything is nicer that way- a cubic centimeter of water is 1 mL.