I haven't had any luck with using cheap solenoid valves on the vacuum side of the pump. They seem to need a minimum amount of pressure to open, which does no good when you are trying to dump the sap directly to the tank.
It's definitely louder and vibrates more, which makes me think it will be short lived, but at the price you can get them for from eBay, you can buy 4-7 of them for the price of one ShurFlo 4008. This makes me more likely to use them for the small clusters of trees that are separated by great distances from larger clusters.