Be sure to consider how much pressure it can handle, what size aggregate it can pump, and how soon you can get replacement parts. Selection of a grout pump should be made with care. Pumps vary so much in power, complexity, and price that to find the one most cost-effective and suited to a masonry contractor's needs requires thorough research. Certain criteria should be clarified before making the purchase. First, what price range is acceptable? Second, what applications will the pump be used for? And third, how often will it be used? The last consideration is crucial to deciding whether the investment should be made in a grout pump at all or whether, in the long run, it would be more cost-effective to hire subcontractors, rent grout pumps, or pour grout. There are two basic types of grout pump--mechanical and hydraulic. Mechanical pumps are less expensive, have lower capacities, and have more moving parts than hydraulic grout pumps. Some mechanical pumps achieve over 400 psi and can pump up to 100 feet vertically. Typically that's sufficient capacity for a contractor that wants to do low-lift grouting. On occasions when high-lift grouting is preferable, the firm can rent a hydraulic unit. However, when more cubic yards of grout need to be pumped per hour (for instance, on multistory buildings), hydraulic pumps can pump 30, or even 60, cubic yards per hour at pressures over 1000 psi. The higher-volume pumps, combined with a higher psi, pump more grout further both horizontally and vertically. Mechanical grout pumps have ball valves and are belt-driven. The internal mechanism includes moving pistons inside a cylinder, the motion of which pulls the grout down from the hopper (loaded with grout from the ready mix truck) and drives it out through the hose into the masonry wall. Hydraulic grout pumps have fewer moving parts and are powered by larger engines. A hydraulic pump transfers more horsepower to the pumping action that pushes grout through the hose. Variable-speed volume selectors of hydraulic pumps make high-lift grouting easier because the operator can regulate the volume as additional stories are added to the building.