Patent ID: 7497274

Claim:
A hydraulic fluid tank for a drilling machine which tank has a tank volume, said drilling machine including a hydraulic pump having a pump suction port which includes a pump suction centerline, wherein the tank comprises: (a) a primary chamber that is located entirely below the hydraulic pump, said primary chamber having a primary volume; (b) a secondary chamber which is: (i) located above the primary chamber and has a secondary volume; (ii) in fluid communication with the primary chamber so that the primary volume of the primary chamber and the secondary volume of the secondary chamber together provide the tank volume to receive and hold hydraulic fluid; (iii) adapted to maintain a hydraulic fluid level that is above the pump suction centerline as the hydraulic fluid in the tank reaches its normal operating temperature during operation of the drilling machine; (iv) sized and configured to allow for thermal expansion of hydraulic fluid in the amount of at least about 5% of the tank volume as the hydraulic fluid in the tank reaches its normal operating temperature during operation of the drilling machine.