Measuring a Big Bore and Standard Bore Rear Cover
Measuring an STX standard bore 8" rear cover and an STX big bore 6" rear cover

One of the benefits of owning an ANSI B73.1 process pump is the ability to buy replacement pumps or parts from your choice of vendor. But just as you would need to know the make, model, and year of your car to buy replacement parts, you also need to know the brand, model, and size of your pump to ensure that the parts you are buying will fit your existing pump.

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Brand: Parts May Not Interchange Between Brands

Although the pumping unit of an ANSI pump are interchangeable between brands according to the dimensional standards of ANSI B73.1, the individual parts that make up the pump may not necessarily interchange between brands. Do your homework before buying a replacement part and make sure the replacement parts will interchange 100% with the pump you have. Parts from OnHandSupply interchanges with the Goulds 3196 style of ANSI pumps, but does not interchange with Flowerserve Durco Mark III style.

Model: Replacement Parts are Model Specific

The model number identifies whether or not you have an ANSI pump. For example, Goulds makes many different types of pumps besides the ANSI pump, but only their model 3196 is the ANSI B73.1 line. Pay close attention to any letters or suffix in the model number, as it may indicate a specialized model whose parts may not interchange with other brands.

Some parts may interchange between models, most commonly the power end. Although Summit's 2196 is their ANSI pump line and their 2196R line is not, the 2196R model uses the same power end. The same goes for Goulds, who use the same power end for seven different pump models

Size: Some Parts are Size Speicifc

Pumps come in different sizes, and you need to know the size of your pump to order the right part. The pump size looks like this:

How to Read a Pump Size

Your pump size tells you whether your pump is in the STX series, MTX / LTX series, or XLTX series (think Small, Medium, Large, and Extra Large). Each size in the ANSI line has a unique impeller and casing. The rear cover (or stuffing box) and the adapter is shared among sizes with the same max impeller diameter within a series. The pump size also determines what size foot to use.

Once you have the brand, model number, and size, you're almost set. Here are some additional details to consider:

  • Is your pump MTX or LTX? - MTX and LTX (Medium / Large) series share the same sizes, so things can get confusing. Although they share the same size, they use different power ends and rear covers. You can distinguish which series your pump is by measuring the shaft diameter of your existing pump:

    STX MTX LTX XLTX
    Shaft Diameter 1.375" 1.75" 2.125" 2.50"

  • Is your rear cover (stuffing box) a "standard bore" or "big bore"? - You need to know this if you are replacing your rear cover or if you are replacing your sealing mechanism. Mechanical seals are different for standard bore and big bore configurations. Packing cannot be used in big bore rear covers. Measure the inside of your seal chamber and compare with the table below.

    STX MTX LTX XLTX
    Standard Bore 2.00" 2.50" 2.875" 3.375"
    Big Bore 2.875" 3.50" 3.875" 4.75"

  • Check if your impeller was trimmed down - When a pump size is recommended for an application, an impeller may be trimmed down from its original size to optimize pump efficiency. If the serial plate does not have the trimmed diameter size, measure from the eye of the impeller to the furthest point on one of the impeller vanes to determine the radius, then double it for the diameter.