Drill Master: Paying Attention to Your Mud Pump
The industry is in another economic turndown but hopefully not as severe as the last. It is a fine time to look at ways to stretch ones working capital. It is my opinion that there is less attention paid to the mud pump (water pump as some would call it) than any other mechanism on the rest of the HDD rig. I am outlining procedures below that will greatly enhance the life of the pump.
There are ways to ensure a long life out of the pump if a little practical maintenance is performed on a regular basis. One of the first areas to look at is the type and quality of oil that is used in the power end of the pump. Always follow the manufacturer’s recommendation as to the type and viscosity. There are synthetic oils available that will meet the specification of the manufacturer and will not emulsify with water. Since HDD work is intermittent, the pump is always heating and cooling. This activity will cause moisture to build up over time in the power end. The consequence of fowled oil is catastrophic failure of the power end. The majority of pumps in the HDD industry do not hold a great deal of oil. Changing the oil every six weeks to two months will make the rig owner money.
Check for slack in the connecting rod pin and pin bushing by disconnecting the piston rod from the pony rod. Push back and pull out on the pony rod to determine if there is any slack. If you feel slack, it is coming from either the pin and bushing area or the connecting rod bearing. Further inspection of the power end components is required. Slack in either the connecting rod bearing or the pin and bushing or a combination of both will yield extended run out at the piston and will greatly reduce piston life. At the same time, this slack will prematurely wear out the wiper box packing. While performing this task, it is an excellent time to inspect the wiper box packing. This packing is relatively inexpensive and should be kept in new condition at all times. If one finds that a pony rod is scoured, it should be replaced. The wiper box area is a direct path for contamination to enter the power end.
For the most part, reciprocating pumps internally are less complicated than a single stroke gasoline engine. There are a few checks that are easy to do to ensure the internal components are sound. The crankshaft end play is critical. To check, remove the inspection cover on the rear of the pump. Force the crankshaft side to side to ensure the end play or run out is within manufacturer specifications by using a magnetic dial indicator. If it is out of tolerance, re-shim the crankshaft. This procedure will lengthen the operating life of the pump unless the main roller bearings and cups are worn to the extent that shimming is no longer feasible. If that is the case, the roller bearings and cups will need to be replaced.
Remove the individual rod caps and inspect the journals on the crankshaft. Most manufacturers use either precision or shimmed connecting rod bearings. Measure the journals and check for wear or egging on the crankshaft. The manufacturer will list a new and a throwaway dimension. If the crankshaft journal is close in tolerance but is grooved, lightly sand the journal to smooth it and install a new connecting rod bearing. Always use a torque wrench and torque the rod cap studs to the specifications given in the owner’s manual. Since a reciprocating pump runs relatively slow, sanding a journal will work and lengthen the overall life of the pump.
If wear was not indicated on the crankshaft journals, then any slack would have to come from the crosshead pin and pin bushing. Most reciprocating pumps will have to be totally torn down in order to reach this area. However, it is not a difficult task to remove the crankshaft, which will allow access to the cross head. The new pin bushing will have to be honed to accept the new pin. A press will be required to both remove and install the new pin. When either removing the old pin or installing the new, be careful to press straight down otherwise it is possible to egg shape the crosshead. Again, follow the manufacturer’s recommendations concerning tolerance.
These practices seem simple and they are. If one performs the tasks above once or twice a year, he will extend the overall life of the unit and greatly reduce his overall operating cost.
Ron Lowe is regional manager with Myers Aplex, a Pentair Industrial company, and a member of the Drillmaster Advisory Board. All Drillmaster Reports are reviewed by the Drillmaster Advisory Board: Lowe; Frank Canon, Baroid Industrial Drilling Products; Richard Levings, Ditch Witch; Ed Savage, Vermeer Corp.; and Trevor Young, Tulsa Rig Iron.
