How do I switch the Topeak mini master blaster pump for presta valve operation? It looks like there's a plastic washer that needs to be reversed but it's impossible to remove.

You are most likely using the pump set up to work with a Schrader valve when you should be using it with the internals set up to work with a Presta valve. This video will help you identify the valve type and explain how to change the internals of the pump: http://www.topeak.com/pages/368/news/detail/832
This video will explain how to change a flat:http://www.topeak.com/pages/368/news/detail/830

I hope this helps, Eddie O - Topeak Inc

If by no pin on the inside and it won't work with the short stubby valve that just means it's ment for a presta valve. Return the pump and get one that works with a schrader valve.

You can buy an inexpensive adapter to fit on either valve stem to convert it from Presta to Schrader or from Schrader to Presta - whichever is better suited to your pump and/or your other bikes. If you want to go with Schrader as your standard (the fatter one) you can replace the tube on your wheel that has the Presta valve - but you have to enlarge the hole in the rim. If you do that be sure to make the edge of the enlarged hole nice and smooth with sandpaper. If you want to standardize on Presta, you will need a small bushing to make the existing hole in the rim smaller. I hope you found this helpful. Good luck, Al K

There are several parts see photo , part 11 is reversed to accept the different valves ie: presta/ Schrader

If it is not a Presta pump, then you will need an adapter. These adapters usually run for less than a dollar and are easy to use. You can just screw it onto the Presta valve and then it converts it to a Schrader. You can see what they look like HERE. They should be available at any bicycle, camping or hiking store. Good luck and be safe riding! (Helmets are your friend)

The pump will work with both types of common bicycle valve.

Yours is the presta, the one like on a car is a schaeder valve.

To inflate or deflate a presta valve you must first "open" the valve by unscrewing the little tip. once it is loose, give it a couple taps to make sure it is not stuck and try pumping again.

If it still does not work, then you may need to reconfigure the internal washer inside the pump, if yoiu don't have the instructions that came with the pump, then I would suggest taking it back to where you puchased it, the shop or any shop for that matter willl be happy to give you a quick demonstration and make sure the pump is configured properly. The pump will work with your valve.

http://www.ehow.com/how_4779541_inflate-bicycle-tire-presta-valve.html

1. Rotate the wheel so the valve is resting just above the floor. Remove the valve cap.
   

2. Unscrew the locking nut on the valve stem. Quickly press down the stem to loosen the seal. You should hear air escaping when the stem is pushed in--if you do not, loosen the nut and try again.
3. Press the pump head onto the valve and flip the locking lever to make a seal. You'll hear air escape, but it should stop after you've locked the lever. If air continues to leak out, remove the pump head and reattach it.
4. Make two pump strokes and listen for air moving into the tire. If the pump handle becomes hard to press down after only a few strokes, or if the pressure gauge elevates extremely quickly, remove the pump head and repeat Step 3.
5. Inflate the tire to its recommended pressure. Remove the head by unlocking its lever and quickly pulling it off the valve stem. Secure the valve's locking nut and cap.

Read more: How to Inflate a Bicycle Tire With a Presta Valve ' eHow.com http://www.ehow.com/how_4779541_inflate-bicycle-tire-presta-valve.html#ixzz1Brv5VfAX

They should be designed to fit both styles of valve, but you need to reverse the seal.
you should be able to unscrew the end, remove the sealing rubber and a plastic fitting that pushes on the valve, replace them the opposite way around ,and they will fit the presta.

remove the cap, pull the rubber bit out, tap out the green bit, then switch it round, but this is where your problems start, as it does not seem to pump the tyer up.

Change the internal parts of the head to adapt to the valve type you're using.

http://www.bikenewyork.org/resources/nuts_bolts/tires.html

See solution 2