A transfer pump is a pump used to transfer fluids. It’s just a name and can be any type of pump. It can be a 12 volt pump ran off of a battery, a 120 volt pump that plugs into a receptacle, a pump ran off a gas engine, or even a manual pump that you pump with your hand. It’s just any pump that you use to transfer fluid from one container to another. If you mainly transfer your fluids at home a 120v pump would probably be easier. If you transfer while on jobs a 12v pump would be the way to go.
As far as a 12 gpm transfer pump sure, it’ll just transfer fluids faster than your 5.3 gpm pump. As far as using a 12 gpm pump to force feed your injector I would imagine that’s way too much. There aren’t that many people who force feed their injector but I’ve heard something like a 2 gpm pump is enough to boost your sh percentage quite a bit when down streaming. I’m not sure if Alex has done it but I know I’ve heard him talk a little about it so maybe he can chime in. @Infinity I don’t see why you would need anything larger than a 5 gpm pump to transfer fluids but the bigger you have the faster it’ll transfer. A 5 gpm pump will only take about 10 minutes to transfer a whole 55 gallon drum of sh to another. I think if I were you I’d get a 7 gpm 100 psi 12v for your roof pump and just use the 5 gpm as a backup and a transfer pump. Most don’t force feed their injector they just pull out their roof pump when they need a stronger mix. Nothing run with force feeding if it works for you. When do you have to force feed? Stucco or brick? You should downsize your injector to a 2-3 gpm instead of the 5-8 gpm you’re currently using. You’ll get a stronger mix that way even if your pressure washer is a 5.5 gpm or 8 gpm.
As far as a 12 volt booster pump I’m not entirely sure. There are only a few guys that even run them on here. I’m sure they make 12v booster pumps. @Diamond_Soft_Wash comes to mind with the booster pump. His runs off a generator or he plugs it into the customer’s house. I’m sure they make a booster pump that runs off batteries but it might not be feasible for our use. Maybe Mike can answer that if he sees that I tagged him.
Some guys run a pump that is powered by an air compressor. Just search for AODD pump.