Custom Masters/Flo King
Phone: 407-331-4634
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Flo King BXL2500 & BXL5000 Materials of Construction

BXL2500-BXL5000 MaterialGeneral guidelines for selecting the Low-Profile BXL2500 and BXL5000 pump material of construction are shown below.

Disclaimer: This is a general guide based on user operating experiences with Flo King Filter Systems. The information presented may not be suitable for every application.

CPVC as Pump Material of Construction
CPVC (gray in color) is our standard, least-expensive, and by far the most popular pump material of construction for the Low-Profile BXL2500 and BXL5000. CPVC is generally recommended for neutral solutions and many acids at a wide range of temperatures.

CPVC is also often used in mildly alkaline solutions at temperatures up to 160-180 (71 to 82 C). However, CPVC may become brittle, then crack and split, in some highly alkaline solutions, even at relatively low temperatures (examples: alkaline non-cyanide zinc or aggressive, highly caustic alkaline cleaners).

CPVC applications for the low-profile BXL2500 and BXL5000 include: nickel electroplating, acid copper plating, acid tin plating, acid zinc plating, chromating, decorative chrome plating, passivating, pickling, rinsing, anodizing, low-temperature seals, mild alkaline cleaners. Many customers use CPVC in cyanide silver, cyanide copper and cyanide zinc, though some prefer polypro.

Polypropylene as Pump Material of Construction
Polypropylene (white in color) can also be used in neutral solutions and some acids at a wide range of temperatures.

Polypropylene is generally satisfactory for mild to moderately aggressive alkaline solutions at temperatures up to 160 - 170 F (70 - 77 C). However, at temperatures well above 170 F (77 C) or in highly concentrated, high-pH caustic solutions, polypropylene may swell, causing serious pump problems. In cases of aggressive caustics — especially at higher temperatures — only stainless steel pump construction is recommended.

Polypropylene is readily attacked by concentrated chromic acid and cannot be used in applications such as hard chrome plating or chromic acid anodizing.

Polypropylene costs about 10 percent more than CPVC for the BXL2500 and BXL5000.

Typical polypro applications include: alkaline non-cyanide zinc plating, zincating, mild alkaline cleaners

Kynar (PVDF) as Pump Material of Construction
Kynar is a high-temperature plastic that can be used in neutral solutions up to about 215 F (105 C) and also in many acids at higher temperatures than CPVC can withstand.

However, like CPVC, Kynar is absolutely not recommended for highly aggressive alkaline solutions. It tends to become brittle, then crack and split in aggressive caustics.

Kynar applications include: concentrated chromic acid solutions, electroless nickel solutions well above 190 F (88 C), high-temperature seals following anodizing (sometimes up to 212 F, 100 C)

Kynar is expensive — from 40-50 percent more than CPVC and 30-40 percent more than polypro for the BXL2500 and BXL5000, depending on required accessories.

Stainless Steel as Pump Material of Construction
Stainless steel (SS) is the material of choice for highly aggressive alkaline solutions at high temperatures — typically from 180 to 200 F (70 to 93 C).

Typical SS applications include: caustic high-pH cleaners, caustic strippers, caustic permanganate solutions, and black oxide (up to about 205 F, 96 C).

The BXL2500 and BXL5000 are available in stainless steel, but only in the 12-inch-long pump-body length. Depending on accessories required, the SS BXL3000 and SS BXL5000 cost about 130 to 135 percent more than CPVC, 120 to 125 percent more than polypro, and 55 to 60 percent more than Kynar.

Most customers use SS pumps strictly for recirculation (without filter cartridge attached).


There are many solutions in which the Flo King system is effective.

Click this link to see pump material recommendations for many popular electroplating and other metal-finishing applications.


BXL2500-BXL5000 Shaft MaterialUnless otherwise specified, all Flo King pumps have an internal shaft made of 303 stainless-steel covered with Teflon heat-shrink tubing. In most cases, this works well, but when there is a failure, it almost always occurs when aggressive acids attack the SS Shaft where the Impeller screws onto the Shaft threads. This may happen because of (1) pinholes or other imperfections that develop in the Teflon coating, (2) wear and tear over time, or (3) objects that are sucked into the pump and damage the Teflon heat-shrink tubing. Caution: If using the pump strictly for recirculation (without filter cartridge attached), always install a Pump Strainer Adapter (PSA) to protect the Impeller, Shaft, and Teflon heat-shrink tubing from damage due to any foreign objects that might be in solution. See this link for PSA photo.

When to Consider Alternative Internal-Shaft Materials: If a solution is known to aggressively attack stainless steel, an internal titanium-tip or Hastelloy-tip Shaft is strongly recommended as a precaution for the BXL2500 and BXL5000. One end of the tip is threaded onto the SS shaft and the other end onto the Impeller to provide additional protection. All Shafts are covered with Teflon Heat-Shrink Tubing.

   • Some Titanium-Tip Internal-Shaft Applications: Solutions containing sulfuric acid and chromic acid

   • Hastelloy-Tip Internal-Shaft Applications: Hastelloy C276 is a nickel-chrome-molybdenum-tungsten alloy that has better resistance to fluorides than does titanium. It is the customer's responsibility to determine if the solution attacks both stainless steel and titanium. If you are unsure if Hastelloy is needed for your application, we suggest you contact the chemical supplier for advice.

There are many Chemical Resistance Charts available on the internet. We encourage you to research those charts for plastic and metal compatibility information if you do not find what you need here.

Four Materials

CPVC (gray in color) is our standard, least-expensive and most popular pump material of construction for the Low-Profile BXL2500 and BXL5000. Polypro (white), preferred for some applications, costs more. For rare, special applications, Kynar (PVDF) and stainless steel are also available.