What was found
FLIGHT 7835 - CMH-IAD - EN ROUTE FROM CMH TO IAD, RECEIVED HYD 1 LO QTY MESSAGE ON EICAS. LATER, RECEIVED E1 HYD PUMP FAIL AND HYD SYS 1 FAIL ALONG WITH ALL ASSOCIATED MESSAGES. COMPLIED WITH THE QRH AND INFORMED OF ATC OF THE MECHANICAL FAILURE AND DECLARED AN EMERGENCY DUE TO NR 1 HYD SYSTEM FAILURE. ON APPROACH, THE SYSTEM PARTIALLY RESTORED ITSELF AND A/C WAS ABLE TO EXTEND THE GEAR USING NORMAL MEANS. LANDING WAS UNEVENTFUL AND HAD NO PROBLEMS STEERING THE AIRCRAFT ON THE GROUND. REMOVED AND REPLACED NR 1 ENGINE DRIVEN HYDRAULIC PUMP. OPS AND LEAK CHECKS GOOD.