To reduce the tolerance bandwidth, tighter manufacturing tolerances are required, which add cost and may increase delivery time. Sand-cast molds are the least expensive to make but typically have the widest tolerances. Investment casting will have the best finish and the most repeatable dimensions. The molding equipment cost for an investment casting may be two to four times that of a sand mold. It takes a high production volume to justify the cost of this casting equipment. To have a smaller bandwidth when sand casting may require many hours in hand labor to obtain the exact results from one pump to another.
Reduction of the tolerance bandwidth for measuring the tolerances will add costs and may increase delivery time. This results from using more sophisticated test equipment and an extension of the actual test period to get a higher stability of the operation point.
Table 1. Recommended test specification matrix
The recommended test specification matrix shown in Table 1 is intended to be used as a guide to help users decide which tests should be specified based on pump power and intended service. For normally manufactured pumps, end users may consider a certificate of compliance in place of actual testing.
The definitions for Table 1 are:
Standard pumps—Pumps that have previously been manufactured and have a history of consistently demonstrated compliance with HI test standards
New/unique design—Pumps of a new size or with new design features
Critical service or application—As defined by customer
For more information on this topic, look to ANSI/HI 14.6, Rotodynamic Pumps for Hydraulic Performance Acceptance Tests.