As hydraulic fluid power industries return to business amid the COVID-19 crisis, it is key to take care when restarting hydraulic machinery that you do not do more harm than good. When hydraulics sit for weeks or months at a time, they need special care before startup. In this article, we will discuss procedures and checks for a more effective startup.
CHECK #1: Check That Pump Spins Freely
The most important thing to check first on positive displacement pumps is that the pump still spins freely. It’s possible the pump could contain solidified product or have mechanical issues from sitting idle.
To check this, lockout the prime mover, remove the coupling guard and turn the shaft. Listen for rubbing sounds. Most centrifugal pumps should turn by hand. If the pump doesn’t turn, don’t force it. Instead, take it apart and inspect.
On positive displacement pumps, the shaft may be difficult to spin. Do not use a pipe wrench to assist. Using a pipe wrench will damage the shaft and could cause additional damage to other components. A strap wrench will suffice if necessary on a large centrifugal pump or positive displacement pump.
CHECK #2: Check Couplings and Mechanical Seals
Since the coupling guard is off, now is a good time to check the condition of the coupling. Look for evidence of wear. This could include rubber dust or plastic chunks under the coupling. This is evidence of misalignment; the pump should be re-aligned before re-starting. Inspect the mechanical seal for leakage. If there is flush water to the mechanical seal, make sure it’s turned on.
CHECK #3: Take an Oil Sample
Take an oil sample on all machines and filter or flush all units if needed before start-up. If a machine has been out of service for a period of time then condensation can form and cool off increasing the water content in the oil and hurt performance. If necessary, fill the pump case with clean oil.
CHECK #4: Check Hoses, Clamps and Connections
All hoses, clamps and connections should be inspected and tightened if necessary. Loose connections will become leaks in time. The pumps should be re-primed as oil could have leaked out through the seals or drained back to the tank through the clearances in the pump.
CHECK #5: Double-check Valves and Filters
After the pumps and hoses have been inspected, double check and ensure all hand valves that need to be open are open. That includes all pressure and return line hand valves you may have as well as all suction line hand valves. Leaving the suction line hand valve closed will cause the pump to cavitate and will rapidly destroy the pump. Check suction, pressure, and return filter. Replace dirty filters as needed.
CHECK #6: Prime and Vent the Pump
Make sure valves are in the correct position and pump is primed and vented. Ensure suction valves are open and liquid is at the pump. Discharge valves should be 10-15% of full open. Now that the suction valve is open, liquid should fill the pump and prime it.
CHECK #7: Inspect Base
Now that the pump is almost ready, do a final check of the base to ensure that mounting bolts are tight. There should be no soft feet on the pump or motor. Baseplate pads should be level to within .002” per foot and the maximum out of level from one end to the other should not exceed 1/32.”
CHECK #8: Start-Up and Final Check
Now that all of those pre-startup checks have been made, it is safe to turn on the system. Once the pumps are on, check the compensator settings. Also check the relief valve for bypassing and that it is set to the correct pressure. If the relief valve is bypassing, reset the pressures in the system to correct the issue. If is it sill bypassing, the valve must be replaced. The final step is to inspect all lines and components for leaks. If a leak is found, take all necessary steps to fix it. To further prevent overheating, take care to clean the tank and valves of dirt and dust, as a buildup of this will act as an insulator, trapping heat in the system. Finally before starting up, make sure that all cylinder and motor mechanical linkages are in proper working order.
Steve Downey is an Adjunct Fluid Power Instructor at Henry Ford Community College and Macomb Community College. He has worked in the Fluid Power Industry for 30 years in both Industrial and Mobile Hydraulics. Steve Holds 11 International Fluid Power Society certifications.