O ring problems with APH/CPS pump

Build a homemade water gun or water balloon launcher and tell us about it.
Locked
affrothunder
Posts: 4
Joined: Wed May 20, 2009 4:57 am

O ring problems with APH/CPS pump

Post by affrothunder » Sun Jun 07, 2009 3:44 am

I tried to make a pump, but the O-ring keeps sliding off. I know the article on making the pump on the APH instructions page says that this means that the cut in the wood is too deep (I think it meant this), but even if I try a shallower groove it still doesn't work. I've tried smaller o-rings but they just slip through. Do I need to just keep experimenting with grooves or do I need to soak the wood longer (I put the o-ring in the groove and soaked the wood for a minute or two)? Also, how big is the o-ring supposed to be in relation to the opening of the PVC pipe. Should it just barely fit in or be larger/smaller than the opening? Lastly, is Vaseline or grease recommended (since one of the links on a pump construction page on the site said to use lots of Vaseline)?

User avatar
Silence
Posts: 3825
Joined: Sun Apr 09, 2006 9:01 pm

Re: O ring problems with APH/CPS pump

Post by Silence » Sun Jun 07, 2009 4:05 am

Wrap a good amount of tape around the rod on both sides of the O-ring to hold it in place. Most people use electrical tape, but duct tape is probably better if you can cut it easily enough.

The O-ring should be a tiny bit larger in order to produce a seal. The difference may be unnoticeable, but it should fit with some resistance. Hard to say. Lube will help the seal and make the pump easier to move – I used to recommend only silicone lubricant (since oil-based lubes can damage rubber), but Vaseline is probably okay (since O-rings are generally synthetic, and APHs don't use rubber bladders).

User avatar
SSCBen
Posts: 6449
Joined: Sat Mar 22, 2003 1:00 pm

Re: O ring problems with APH/CPS pump

Post by SSCBen » Sun Jun 07, 2009 1:26 pm

When the wood pump works it works great. Sadly others haven't replicated my success. Maybe the wood available to me is slightly off the correct and more common diameter.

We'll have to figure out better ways to construct pump seals. My suggestion would be to read this O-ring design guide, and figure out which materials and O-rings will work based on what's available (McMaster-Carr is a good start).
Last edited by SSCBen on Sun Jun 07, 2009 6:15 pm, edited 1 time in total.

User avatar
Drenchenator
Posts: 807
Joined: Fri Jun 18, 2004 12:00 pm

Re: O ring problems with APH/CPS pump

Post by Drenchenator » Sun Jun 07, 2009 1:33 pm

If you don't want to use tape, try doing what I did in this article on the site. I epoxied plastic rings to hold three O-rings in place. I always thought that tape was a bad idea in the first place.

Getting the right size O-ring is very important. Measure the pipe's inner diameter and your pump rod's outer diameter and try to get O-rings that have an inner diameter slightly smaller than the pump rod's outer diameter, and have an outer diameter slightly larger than the pipe's inner diameter. Also ensure that your final pump is well-lubricated; the right size O-rings will always resist movement, but lubrication removes this problem in its entirety.
The Drenchenator, also known as Lt. Col. Drench.

Tyler
Posts: 20
Joined: Fri May 29, 2009 3:35 am

Re: O ring problems with APH/CPS pump

Post by Tyler » Sun Jun 07, 2009 1:56 pm

Hey go with Drenchenator's pump, it takes a bit longer to make but it works well once to get it done.
When you make it, you can still cut the groove in between the cpvc for the o-ring(s), I only had success with one o-ring so far, but it works. Also, for me it works better not to cut the cpvc pieces with scissors but just to slide them over the dowel. After the cpvc pieces are glued and dried the wood will expand on each side of them and will prevent them from sliding up and down. (After being exposed to water)
Also the o-ring size listed in the 'manual' worked just fine for me.

User avatar
C-A_99
Posts: 1502
Joined: Tue Aug 01, 2006 11:09 pm

Re: O ring problems with APH/CPS pump

Post by C-A_99 » Sun Jun 07, 2009 4:16 pm

Never, ever, use scissors to cut pipe nor rods. As for the CPVC, the one available here (1/2") is too large to fit into 1/2" PVC (the standard for pumps) and yet too small to fit onto 1/2" dowels. It can be cut and grinded, but thats a pain, so I'm now trying to get tape to work. Duct tape might hold up (I haven't tried it but heard it works) but electrical tape will get pushed out. However, e-tape is good if you need to artificially increase the OD of a dowel.

User avatar
cantab
Posts: 1492
Joined: Fri Oct 19, 2007 1:35 pm

Re: O ring problems with APH/CPS pump

Post by cantab » Sun Jun 07, 2009 5:47 pm

Electrical tape will NOT resist water. To be honest its mechanical and adhesive properties are generally poor.
I work on Windows. My toolbox is Linux.
Arsenal:
Super Soaker: XP215, 2xXP220, Liquidator, Aquashock Secret Strike M(odded), Arctic Blast M, CPS1200, CPS2100, SC Power Pak, 3l aquapack, 1.5l aquapack
Water Warriors: Jet, Sting Ray M, Shark, Argon M, Tiger Shark, PulseMaster
Others: Waterbolt, The Blaster, Storm 500, Shield Blaster 2000, generic PR gun, generic backpack piston pumper (broken), 3l garden sprayer M, 10l water carrier:

User avatar
Drenchenator
Posts: 807
Joined: Fri Jun 18, 2004 12:00 pm

Re: O ring problems with APH/CPS pump

Post by Drenchenator » Sun Jun 07, 2009 9:10 pm

C-A_99 wrote:Never, ever, use scissors to cut pipe nor rods.
I think I actually used pliers to cut the small pieces of CPVC. The scissors part appears to be a typo after the fact. Still, I don't see anything wrong with using scissors; the plastic is very thin anyway and cutting it wouldn't hurt the scissors in the slightest. It's not like we're talking about using scissors to cut 3" schedule 40 PVC--in fact, we're cutting the smallest plastic pipe available at my local Lowes!

In the end, step 1 discusses using a saw to cut the pieces perpendicularly to the pipe; step 2 discusses cutting parallel to the pipe to open the piece up slightly. C-A_99 is right: 1/2" CPVC is too small to fit over 1/2" dowels and too large to fit into 1/2" schedule 40 PVC pipe. But if it's cut parallel to the pipe, it slips right over the dowel for easy bonding later.
The Drenchenator, also known as Lt. Col. Drench.

User avatar
C-A_99
Posts: 1502
Joined: Tue Aug 01, 2006 11:09 pm

Re: O ring problems with APH/CPS pump

Post by C-A_99 » Mon Jun 15, 2009 7:45 pm

Pliers and heavy duty scissors may work for 1/2" CPVC, but I still prefer my PVC cutter. As for slipping CPVC over 1/2" dowels, I never thought about cutting parallel a few years ago when building my CPH, I just drilled and grinded out the inside. Either way, dremeling or sandpapering the outside of the CPVC is still necessary for it to fit in the pipe. Cutting the CPVC spacers well is also important so the O-rings fit in properly.

As for e-tape, it seems to hold up for some time before breaking up. If the tape is applied directly to the rod and doesnt layer up too high, it will generally stay in place but will probably break up during heavier use. It will always break up if something is pushing it, so I'm only using it as an under-layer to O-rings whose ID's are too large for a given dowel.

Locked