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MATWELD, INC. PHONE:(270) 444-0085 FAX:(270) 443-6180
Matweld reserves the right to change parts, features, or specifications without notice.
Rev. 02/10
REVIEW OF HYDRAULIC PRINCIPLES
A. TOOL CIRCUIT
1. HYDRAULIC FORMULAS:
CID X RPM GPM X PSI
GPM = 231 HP = 1714 (.85)
1456.9
Example: HP required to deliver 10 GPM at 1500 PSI.
10 GPM X 1500 PSI = 15000 = 10.3 HP
1456.9 1456.9
(subtract back pressure for tool HP)
Estimated HP delivered by pump or used by tool.
PSI
GPM 500 1,000 1,500 2,000 2,500 3,000
3 1.03 2.06 3.09 4.12 5.15 6.18
5 1.72 3.43 5.15 6.86 8.58 10.30
10 3.43 6.86 10.3 13.70 17.20 20.60
15 5.15 10.30 15.40 20.60 25.70 30.90
2. BACK PRESSURE
BACK PRESSURE MEASURED AT THE TOOL RETURN PORT MUST NOT EXCEED THE MANUFAC-
TURERS BACK PRESSURE RATING. MOST MANUFACTURERS LIST THE MAXIMUM BACK PRES-
SURE FOR THEIR HYDRAULIC TOOLS AT 250 PSI. BACK PRESSURE MEASURED ON THE RE-
TURN SIDE OF THE TOOL IS THE FORCE REQUIRED TO GET THE OIL BACK TO THE TANK. IN
ALMOST ALL CASES THE LOWER THE BACK PRESSURE THE BETTER THE TOOL PERFORMANCE.
FIRST, THE BACK PRESSURE IS SUBTRACTED FROM THE MAXIMUM TOOL PRESSURE TO AR-
RIVE AT A MAXIMUM TOOL OPERATING PRESSURE. FOR EXAMPLE, TOOLS WITH 2000 PSI OPER-
ATING PRESSURE ARE INSTALLED ON A SYSTEM WITH 250 PSI BACK PRESSURE. THIS LEAVES
1750 PSI AS A MAXIMUM TOOL PRESSURE. IMAGINE A SYSTEM WITH 500 PSI BACK PRESSURE.
2000 MINUS 500 PSI BACK PRESSURE LEAVES ONLY 1500 PSI FOR THE TOOL. SECOND, TOOLS
ARE DESIGNED FOR PRESSURE TO BUILD ON THE PRESSURE SIDE OF THE TOOL. IF TOO
MUCH PRESSURE BUILDS ON THE RETURN SIDE, NOT ONLY IS PERFORMANCE EFFECTED,
BUT SEALS MAY BLOW. THIS IS WHY IT IS VERY IMPORTANT TO DIRECT THE FLOW INTO THE
TOOL CORRECTLY. REVERSING THE HOSES TO TEST MAY RESULT IN BLOWN SEALS, DAMAGE
TO THE TOOL, AND PERSONAL INJURY.
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