There are two type of towable tube, one is partially covered towable tube, the other is fully covered towable tube.
How to fill a partially covered towable tube correctly?
For open top tubes , it is a simple matter of placing the PVC bladder inside the cover and aligning the molded Boston valve with the corresponding opening in the nylon cover. If you haven’t done so already, unfold the PVC bladder and lay it out to roughly match the outline of the nylon cover. Always try to find a clean, debris free area to inflate your tube because sharp rocks, twigs and glass could puncture the bladder or rip the cover.
Unscrew the main body of the Boston valve (or speed valve in the case of the Spin Cycle) and inflate the tube half full. Replace the Boston Valve assembly to stop the back flow of air. At this point, check the alignment of the tube and cover. You can fine tune the tube alignment by grasping the Quick Connect end fitting and shaking the tube back and forth. With a little effort, the tube will just about center itself. Once everything is aligned to your satisfaction, unscrew the top cap from the Boston valve. This 3-way valve has a rubber flapper on the bottom of the threaded stem which allows air to be pumped in but also keeps it from coming back out. So, with the top cap removed, continue to inflate the tube until the nylon cover is fairly wrinkle-free and the PVC bladder feels taut. A tube that is inflated per these instructions will glide across the water and not drag.
Keep in mind that once the tube goes into the cold water, it may feel as if it is losing air. However, it is just the fact that the air inside the tube is contracting. The opposite is true as well: When the tube gets hot from the sun, it will expand greatly. If this happens, adjustments can easily be made: Add a little air if the cover looks sloppy; let air out if things are heating up. Bottom line: Check the inflation level before each use.
Some tube models,use nylon straps that encircle the PVC bladder. The purpose of these straps is to lock the top fabric to the bottom to prevent hands and feet from getting caught under loose material. These straps also help the tube maintain its desired shape. When inflating tube with these ‘control straps’, it is a good idea to lay the PVC tube inside the cover, align the two straps and then join the two ends with the mating pieces of “hook” and “loop” material. The length of the straps has been optimized to fit best when the tube is properly inflated. Once the straps are secured, inflate your tube as instructed.
How to fill a partially covered towable tube?
Larger, fully covered tubes are as simple to fill as the little ones, although there might be a few more steps to completing this process. One of the nice things is that they come pre-assembled. This means the bladder has already been lined up inside the nylon cover before it is boxed. It is now just a matter of adding air. However, I would still advise inflating the tube half full and then checking out the alignment of the cover and the PVC bladder. If the tube has headrests and inflatable seat cushions, it is easier to fill them before the rest of the tube is inflated.
Even if the deck style tube is not pre-assembled, it is an easy process to get this style of tube ready for the water. Un-box your new tube and lay the nylon cover face up on a clean surface. A sandy beach or grass lawn works well. In the middle of the side control gusset (Usually near the back or rear side of the tube), there will be a zippered section. This zippered section will be about 50-70% of the width of the tube. Unfold the PVC bladder and orient this in the same direction as the cover. Now, fold the bladder in thirds lengthwise or just a little narrower than the zippered opening. Slide the front of the bladder through the opening and up to the front of the nylon cover. Then, reaching far inside the cover, simply flip the sides of the folded bladder out towards the sides of the nylon cover. Check the alignment of the Boston valve through the hole in the cover. If they match up, close the zipper, being careful not to pinch the bladder in the teeth of the zipper. Inflate the tube half full and check it out. If needed, grab the front fitting and shake the tube up and down and side to side to center the bladder. If everything is lined up, continue to inflate the bladder until the cover is almost wrinkle free and the bladder is fairly taut.