Why does the pool pump lose its prime when you hook the vacuum into the skimmer?

Blanche, Like a siphon hose, once you get liquid flowing you do not want air to get in or it will interrupt the flow of liquid. If there is air in the line (vacuum hose) and no check valve (which stops this problem), you will lose prime.

IF YOU WANT AVOID LOSING VACUUM WHEN HOOKING UP YOUR POOL CLEANER HOOK POOL CLEANER TO THE END OF THE POOL HOSE TO BE USED (SWIVEL CUFF END). PUT HOSE IN POOL ALONG WITH CLEANER ON IT THEN WHERE THE WATER COMES OUT OF THE POOL INLET PLACE ON INLET FORCING WATER INTO THE THE HOSE FROM POOL PUMP, WHEN THE HOSE IS FULL THE POOL CLEANER WILL START BLOWING OUT AIR FROM THE HOSE AND FLOAT TO THE TOP AND THEN SINK AGAIN ONCE FULL OF WATER, THEN HOOK TO YOUR SKIMMER .IT SHOULD START CLEANING AFTER THAT