In the past months, I have received numerous calls regarding used pumps. People are purchasing them at auctions or on complete machines and hoping to find a diamond in the rough.
In many instances, mud pumps have sat idle in this industry for three years. Given that most of them did not have proper maintenance during the their service life, they sat with emulsified oil for a considerable period of time in extreme weather conditions. This is extremely detrimental to both the power frame, as well as the internal components. Rust could literally destroy a pump on the inside, while the exterior could look reasonably good.
Pumps that run in continuous service generally do not have the problem with moisture forming in the power end. They tend to operate at the same temperature. Also, these type pumps are generally serviced on a regular schedule. Pumps that operate only sporadically will build moisture in the power end even if all their seals are good. The heating and cooling of the unit combined with the relative humidity of the air will form water. This is the precursor of rust.
Just because an auctioned pump may sound cheap, once you factor in the cost necessary to rebuild a power end, it may be more cost-effective to purchase a new power end.
The only way to know what you’re really getting for your dollars is to do a partial inspection. By removing the inspection cover, you can tell a great deal about the integrity of the power end. By running a magnet through the bottom of the cradle, any ground up shavings can be picked up. If there is a large amount of metal on the magnet, it probably would be better to let that one go. Also, pumps sitting for an extended period of time will show signs of rust on the walls of the power end, as well as the crank and other areas. If the power end seems relatively clean, it may be worth purchasing the pump if the price is right.
If the interior of the power end is rusty, it will be necessary to remove all parts and bead blast the interior. After it is properly cleaned, apply a new coat of rust inhibitor paint to the inside and install the power end components.
Of all power end components, the crankshaft will most likely be the most expensive. If the crankshaft is pitted in a few places, it may be possible to use fine emory cloth and polish the journals on the crank. Since a reciprocating pump runs at a slow rpm, a new set of connecting rod bearings may last for a considerable period of time, making this cost-effective.
Crossheads and connection rods can generally be bead-blasted and re-used. Give the connecting rods a good coat of primer and they will probably be as good as new. In most instances, the crosshead pin bushing is a form of bronze and the crosshead pin is hardened and polished steel. If there is any pitting on the crosshead pin or slack in the bushing, they need to be replaced; this area is the smallest and has the greatest load bearing area of the entire power end. This fitting task is a precision task and must be performed correctly.
The main bearings are a critical area. If there is any pitting on either the bearing or the race, they need to be replaced. At the same time, the correct shim setting on the crankshaft is necessary. This information is available from the pump manufacturer, as well all the other torque requirements for the power end components.
The next area to consider is the liquid end. Most of the liquid ends in this industry are manufactured out of ductile iron. Ductile iron is great material; it’s inexpensive and works well in HDD applications. However, there is nothing that can be done with ductile as far as repair. The same can be said for the ductile iron crankshafts.
The remainder of the liquid end expendables, valves, seats, valve inserts, plungers, plunger packing, pistons and liners are replaceable and should not be cost-prohibitive. Since most valve assemblies are manufactured from some form of stainless, they should be able to run again, provided they aren’t washed and are equipped with new valve inserts. The plungers in most cases are some form of ceramic; provided they aren’t pitted or scored, they should be reusable. Plunger packing should be considered expendable and replaced with new.
The same can be said of the pistons. They need to be replaced as time and temperature are their enemy. Piston liners manufactured out of ceramic are probably good to go again. However, if the liners were made out of hardened steel or chrome-lined, they are probably not usable. Stuffing boxes and glands are also a consideration; check to see that the threads on the gland and the stuffing box are reusable.