Compressing soft backpacks

[cantab]

If I have a soft backpack reservoir (like the max infusion pack), and I squash it, will that help push water into the reservoir if there's trouble getting it in otherwise? Is it going to depend on whether the seal between the pack and gun is airtight?

[Ben]

Pushing it will push water out of the backpack, yes. If you have a poor seal though and the water can't go into the reservoir any longer you'll get some leaks though. If the water can go into the reservoir there won't be much leakage if any. Anything you could do to improve the seal would help, but I think the seal from the backpack to the gun would be airtight as to create suction, so you shouldn't have a problem.

[Goldfish4209]

Originally Posted by cantab

If I have a soft backpack reservoir (like the max infusion pack), and I squash it, will that help push water into the reservoir if there's trouble getting it in otherwise? Is it going to depend on whether the seal between the pack and gun is airtight?

What do you mean by "if there's trouble getting it in otherwise"? Like if your pump's jammed or something?

[Silence]

It sounds like maybe the hose and the hose barbs are too narrow. That definitely constricts flow and you fill it when pulling the pump out, at least with some soakers.

Squashing the backpack to increase pressure might work, but bear in mind that if the reservoir is low on water anyway, you'll probably just be pushing the water to a different part of the reservoir. If you're using a homemade backpack (or even otherwise), you might be able to modify it to use a larger hose.

[Drenchenator]

Since most backpacks work using the pressure generated by gravity to get the water into the gun, I'd just recommend either holding the gun lower or the backpack higher and checking the connection to the backpack. If the connection isn't sealed, you can't really suck the water in when pumping and it would have to work completely off gravity. A good seal is vital.

[cantab]

"trouble getting it in otherwise" - if I connect a full backpack to an empty gun, the backpack doesn't just drain straight into the reservoir, at least not very quickly.

(And never mind why I might end up doing that. Just accept that I might.)

[Silence]

That's probably because the difference in elevation is too small, as Drenchenator said. But the biggest problem is that you are trying to fill an empty reservoir. Whereas pumping uses negative pressure (pressure less than one atmosphere - generated when you pull out on the pump) to create a sufficient pressure difference, no such thing exists with plain reservoirs.

[Drenchenator]

But the biggest problem is that you are trying to fill an empty reservoir.

Fill the reservoir a bit; you should notice a difference. When the pump is extended, it creates suction (negative pressure) to pull water into the pump tube from the reservoir. If there is only air in the reservoir, it can't pull in water and won't be able to get much pressure to suck in water from a backpack since the overall pressure won't change too much.