by
lmh » Thu Jan 13, 2022 12:53 pm
... this is all getting a bit drastic! Before changing anything, or dismantling anything drastic, it's worth establishing what's the problem.
It is very easy to disconnect different lines around the injection valve. First check that you know the plumbing diagram for the flow in your autosampler. The 1100 is quite a simple system. With that in mind, you can work out which connections, tubes etc. are most likely to be blocked, by checking which tubes are in use when the injection valve is in the position that's giving you a low pressure, and which are in use when it's giving a high pressure. Someone advised selecting the position of the valve without actually making an injection; this is a good diagnostic idea.
Once you know which part of the path is blocked, you can confirm this practically. Get yourself a little Hamilton syringe attached to some normal Peek hplc tubing (you can get syringe fittings, or you can make one with a finger-tight peek connector around a 1" length of flexible tubing of roughly the same outer diameter as Peek, and an inner diameter just sufficient to fit the syringe needle; use this to seal your syringe-needle to a union, and then attach some peek tubing to the other end of the union when you want to connect it to a port, or just connect the union to bits of tubing if you want to check tubes). Undo a connection, attach your syringe via a bit of Peek, and see if you can squirt water or 50% MeOH through the tube you're aiming to test, and htat it comes out wherever the other end is. So, for example, if you're testing an Agilent 1100 and you think the needle seat might be blocked, raise the needle, take the connection from needle seat to injection valve out of the injection valve, attach it to your syringe, and see if you can push liquid back up out of the needle seat. It should flow easily. If it doesn't, the seat is blocked. You can do this systematically for the whole of the region that you suspect might be blocked. The most likely locations are the needle seat and the connections to the injection valve (not the valve rotor itself, curiously). Dirt gets stuck at restrictions and places where it goes round corners. While you're doing this, be aware of leaks too, ready for when you encounter a system which is managing to stay under the pressure limit by leaking! But almost certainly not in this case!
You will often find that reverse-flushing tubing will get rid of minor blockages. If not, at least you'll know for sure which part is blocked and needs replacement. Merely assuming that the blockage is somewhere because it usually is can be a frustrating way to fix things.
Wear safety specs when pushing solvent through things with a syringe. When they're blocked, and you're trying to see if a blockages is serious or clearable by back-flushing ferociously, if the syringe slips it will spray you in the face with its contents.
But honestly: do test which bit gets blocked. It's quite quick undoing a few connectors to test, and a lot less hassle than changing parts, let alone disassembling a valve (which is almost never necessary).