Insulin Syringe wont draw from vial properly

It could be low pressure inside the vial making it hard to pull the liquid. If you have a loose needle you can stick it in first and check whether air rushes in. Another way is to draw some air into the syringe before inserting it and push that air into the vial to balance the pressure. Don't add too much or the stopper can pop out. The inexpensive syringes might simply be poorly made but it's surprising they would be that bad and still function at all. The cheap ones I tried worked okay.

I ran into the same problem and solved it by pushing air from the syringe into the vial first so it had some pressure. That made the draw work normally.

My recent vials did the same thing. I had to push in a dose worth of air first or the vial would lock up. With no pressure difference and a vacuum there was no fluid movement and the plunger was very hard to pull.

You didn't mention what liquid you're pulling. Some peptides thicken when kept cold. Adding air to the vial before drawing is always helpful. Even then certain peptides still come out only drop by drop. It can be annoying but it does make combining two peptides in one shot easier.

I had the same trouble with my first vials because I didn't vent them right during mixing. It's simple to correct. You can insert just a needle and let the pressure equalize or use the syringe itself to pull air out until the plunger comes free. Doing the venting step while reconstituting stops the issue later.

Have you thought about leaving a venting needle in place while you draw?

I vent after reconstitution and before each dose I push in the same amount of air that I'm about to draw. That gets the liquid flowing.

Whatever your planned dose is, first draw that amount of air and push it into the vial. It really helps. I'm picky about syringes and only use certain 31g 8mm ones. Also if you keep going in and out of the stopper multiple times it dulls the needle and makes later injections painful.

You posted this on 6/3.

I've seen this with some of the thicker or more finicky peptides. Try drawing air into the syringe and pumping it into the vial first to create pressure that helps the draw. If that doesn't fix it then switch to higher quality syringes because cheap ones can have bad needle tips and weak seals that end up costing more later.

Push air in before you draw. That's basic. If the liquid is still too thick you can try a slightly larger needle size.

If you filter into a fresh vial and vent while transferring the liquid there won't be any vacuum left. That's why pushing air in first works. You don't have to remove the syringe, just draw what you need after the air is in.

Draw with a 21 or 22g needle and inject with the 31g insulin syringe.

Since other brands worked fine for you but these ones don't, switching needles seems like the obvious next step. A couple other things could be going on. Needles can bend while drawing or during injection and a crease will block flow badly. Check the rubber stopper on the vial too. Some have a small easy spot in the middle and thicker areas around it, so make sure you're hitting the right part.

The 31g needles do draw slower because they're thinner. Pull the plunger back slowly so you don't create extra resistance that makes it drip. Also when the vial is upside down there can be an air bubble in the neck. If the needle is in that bubble you'll only get air. Turn the vial slowly or give it a light shake to release the bubble before drawing.