Some common goals clients report to me include having a pump that operates reliably for a long time combined with an inexpensive installation. I would argue that it is rare to accomplish both on the same job. Manufacturers often encourage their customers to have a foundation with a mass three to five times the mass of the pump, driver and baseplate combined—even more if the pump is a positive displacement design, especially reciprocating pumps. Additionally, recommendations and specifications focus on ensuring that the baseplate is properly grouted (grouting bonds the base to the foundation).
The purpose of any baseplate is to provide level, coplanar surfaces to mount the pump and driver, allowing for a proper and precise alignment between the two. More importantly, the base provides a path for the transmission of vibrations, nozzle loads and piping forces to the foundation and into the ground. If the base is not designed or installed properly, the investment in the alignment process will be lost in the first moments the pump operates. A proper baseplate installation will maintain that crucial alignment—and pay off for decades with reduced maintenance costs.
I acquiesce that the smaller the pump and consequential horsepower, the need for the expensive installation (foundation, baseplate and grouting) is diminished.
Some companies will buy the least expensive baseplate and then lay it on the floor/ground with no further action other than to pipe up the pump and connect the electricity to the motor. Anyone with pumps that operate in this manner for more than three years with no downtime for bearings, mechanical seals or couplings also has luck on their side. Chances are the pump is lower horsepower, and the service is ambient temperature and at low-duty hours.
Many end users shy away from pre-grouted pump bases or poly pump bases because of their higher initial cost, but anyone wanting a proper installation at an overall and long-term value should consider these alternative choices, especially in the National Electrical Manufacturers Association (NEMA) motor size ranges of 250 horsepower (hp) and below.
This article does not address stilted pump bases.
As an example, a 100-hp pump/driver set is purchased and the next step is installation. A cast iron, Process Industry Practices (PIP) or structural steel base also has been purchased. A good foundation has been designed and it is time to grout the base to the foundation. Here are some tips for the grouting process.
To start, do not assume the mechanical contractor may be the best at the pump installation process. Effectively communicating the specifications and procedures to the contractor increases the chance for success.
1. Prepare the Underside
With no other actions or specifications, almost no pump or base manufacturer will have the baseplate’s underside properly prepared for the grouting procedure. They will have prepared the surface solely to prevent corrosion in the transit and storage stages. Consider these questions: When was the last time you turned the baseplate over and prepared the surface to be grouted? Did you remove the pump and driver?
You can sandblast the underside and then install the base immediately before corrosion occurs (less than eight hours in an ideal ambient). Another approach is applying the proper epoxy paint to the underside as a surface to which the grout can bond. Grout manufacturers will advise the proper surface preparations and paint for their grout.
Many people do not properly prepare the base’s underside surface or they apply too much epoxy paint. Check with the manufacturer, but in most cases 4 mils (dry) is the proper amount. If the paint is too thick, the epoxy grout will pull the paint off of the metal, a process known as delamination. It may be necessary to remove the protective paint supplied by the manufacturer.
In the past, many installations used cementatious grout, but most companies in the last 20 to 30 years have elected to use epoxy grouts. Epoxy grouts yield superior results in most cases, while cementatious grout is less expensive.
2. Remove Equipment from the Baseplate
The equipment (pump and driver) should be removed from the baseplate during the grouting process. Before removing the equipment, make sure it can be aligned and the base is flat and coplanar.
Field machining of the base after completing the critical grouting process is difficult and expensive.
The concrete foundation must be adequately cured before installing and grouting the base. In the case of a new foundation, this depends on ambient conditions and on the concrete mix that was used (a five-bag mix can take as long as 28 days while a seven-bag mix may cure in a week).
Test for moisture by using duct tape to secure a 2- or 3-foot-square piece of plastic over the foundation overnight. Wait longer if moisture is visible on the underside of the plastic the next day.
If installing a base on a new or existing concrete foundation, be sure to chip away the laitance at least one-half inch or, in the case of working an old foundation, until reaching stable concrete or aggregate.
Laitance refers to the thin, flaky layer of hardened yet weak hydrated cement and fine sand on the top surface of concrete, usually from too much water or overworking the surface (for example, resulting from excess trowel work).
When removing the laitance, do not use a jackhammer, which may crack the concrete. Instead, use a small, light-duty pneumatic hammer with a sharp point tip, sometimes referred to as “bush hammering.”
3. Allow Cure Time
Curing time for grout, especially epoxy grout, depends on the ambient temperature. If the site is too hot or cold, steps must be taken to change or control the situation, such as temporary insulated shelters or shade from the sun and heat. Never let rain fall on equipment during this process.
Be aware that during the curing process, the grout can actually pull the base out of level as it shrinks. Continue to check for level during the curing process.
4. Secure Bolts
Most designs require the installation of anchor bolts in the foundation that will run up and through penetrations on the baseplate. This is a highly recommended step. Many believe it is to hold the base to the foundation, but the purpose is to pull the foundation, the grout and baseplate together to form one monolithic mass. Place some tension on the anchor bolts relative to the base when grouting to keep the base from floating.
Do not allow the grout to come in contact with the anchor bolts. Use a protective sleeve/tube with some clearance to allow for tolerances and ease of handling. A common tip is to fill the sleeves with dry sand to prevent the grout from entering that area. The sand can be topped off with caulking or tape.
5. Use Shims & Jack Screws
When I started in the business, we would use sets of wood or metal shims to level the base prior to grouting, leaving the shims in place. Experience has taught me it is prudent to remove the shims after the process because as the shims corrode or rot they will create other issues with the foundation-to-grout joint. If using shims, be sure to apply a coating (such as light grease) of some sort to ease removal.
After some time in the field, I learned to use leveling jack screws in lieu of shims. This technique allowed for more precise results. It was easy if the base manufacturer designed for the use of jack screws, but even when that was not the case, they were easy to adapt and install in the field. If using leveling jack screws, coat them with something (grease) to facilitate their removal. Also, put a piece of metal under the jack screw to prevent digging into the concrete because this makes the leveling procedure very tedious. Small metal plates, preferably stainless steel, can be placed under the jack screw’s nose. These plates are commonly referred to as “pucks.”
Once the jack screws are removed, fill the resultant voids with grout or liquid epoxy.
6. Choose Pour Method
Prior to the grouting process, decide whether to use the two-pour or one-pour method. I prefer the one-pour process, especially if using epoxy grout; it takes a little more preparation time because of the more sophisticated forms, but it will yield excellent results if done correctly.
Keep in mind that when pouring the grout into the forms, the displaced air needs somewhere to go, and that transverse base members and braces can sometimes prevent the proper installation and venting.
I have added (drilled) plenty of vent holes in the base to allow for the venting process.
Typically it is best to pour from one side to let the air escape from the other.
7. Pour Grout
The grout forms need to be strong and liquid tight (do not hesitate to caulk the joints). By comparison, the forms used to pour a patio or driveway are probably not strong enough for this application. Coat forms with something that will not adhere to the grout. A common practice is to use two to three layers of paste wax. Do not use oil because it can react with the grout substrate.
You will not have enough grout if you simply allow for the volume of the form. Prudence suggests you have 10 percent more grout than the form volume—and I guarantee there will
be spillage.
Pour the grout from a head box that is positioned at an elevation higher than the baseplate to provide a static head for the grout to flow.
Try to avoid pushing or rodding the grout into place because it creates air entrainment and voids. It is acceptable to pump the grout in place with different and specific appliances for that purpose. Never use a vibratory device unless specifically directed by the grout manufacturer.
For epoxy grouts, mix the liquid first (resin and catalyst) and then add the aggregate to the liquid mix—not the other way around.
This tip reminds me of my submarine days when the specific instructions were to shut the hatch and then dive the boat. The specific sequence is paramount.
References
“Grouting of Small Pump Baseplates? Is it Worth It?” TAMU Paper 2004 Pump Symposium, Roger L. Jones, Charles A. Lickteig, Jean J. Zoppe
“The Road to Reliable Pumps,” TAMU Paper 2007 Pump Symposium, Todd R. Monroe
“Pump Users Handbook, Life Extension,” Heinz P. Block & Allan R. Budris
To read other articles in the 'Common Pumping Mistakes' column, go here.
