Thought I'd add some results of trying to fix the flow rate on my Trailshot.
Now there's not many bits to the Trailshot, eleven to be precise, so there's not much to go wrong. So this is a sort of a work through in locating the problem.
Was it the filter cartridge? Well I hoped not since that would be almost the price of a whole new Trailshot. A full clean, several times, and things were a little better. I also did MSR's integrity test (Google this, it's an easy test to perform) and everything seemed OK.
Going through how the Trailshot works and also having a known working unit (my wife's) to compare to, I noticed that the priming of the unit was different. You squeeze the bulb about ten times to fill its reservoir - at this point you should get full flow. My unit would only fill to about 20% so when I subsequently squeezed the bulb to get water rather than force the incompressible water through the cartridge I was compressing air hence sod all flow.
No water was escaping from the bulb so it wasn't damaged. I checked the pre-filter and check-valve (a sort of one-way valve) and everything was clear so water could get in. Taking the cap assembly off I happened to try squeezing the bulb and it began filling, a few more squeezes and it filled completely! So the cap was somehow preventing the bulb from working properly, curious. I tried various levels of tightening the cap down with occasionally explosively wet results
I also swapped parts back and forth between the working unit and mine but with no real difference in its behaviour.
All this while my attention had been on the bulb, after all that's where "the problem" lay. Then during one attempt at priming I happened to notice air bubbles escaping from between the male and female parts of the check valve housing. Try the working unit - no bubbles. Hmm. Now I'm beginning to better understand how all the parts work together ...
At either end of the system is a one way valve, the check valve at the input and the umbrella valve in the output cap, both are aligned so that flow occurs from the dirty to the clean side. During priming when you squeeze the bulb air is expelled through the umbrella valve, when you release the bulb the partial vacuum seals the umbrella valve whilst at the same time allowing water to enter via the check valve. Repeat until bulb is full at which point you get full output flow.
A bit of searching about Trailshot priming problems and it seems the above paragraph isn't quite right in that priming doesn't rely on the check valve to work. One suggestion was to remove the input filter and check valve altogether to prime the unit. This works! In fact it only takes three squeezes of the bulb to fully prime it but you need to have the unit with the output valve lower than where the input pipe enters. Taking the end of the tube out of the water to replace the input filter only introduces a little air back into the system. Two potential problems:
1. You might drop the input filter and/or the check valve
2. The initial priming could be using cloudy water with particulates so will clog the filter quicker.
Not an ideal solution but it does mean my unit will work. I thought it might have been my check valve but swapping it for the other one and there's still no improvement so it's possible that there's multiple faults with mine all combining to prevent correct priming.
