Abstract: A vacuum assisted pump priming system which includes a vacuum chamber communicating with a pump inlet via a transfer passage. A valve assembly within the vacuum chamber controls the communication of a vacuum source with the chamber. The valve assembly includes a semi-cylindrical valve body having a plurality of ports by which the vacuum source is communicated with the vacuum chamber. A closure element, attached to a float, is operative to block the vacuum ports when the float rises above a predetermined level in the vacuum chamber in response to liquid entering the chamber. A lost motion connection is established between the float and the valve body, which enables the float to rise above the predetermined level, while the closure element maintains its blocking relationship with the ports. The float includes an enlarge portion that acts as a defuser and a tamper portion which is received in the transfer passage and is operative to dislodge matter drawn into the transfer passage.