Solution pump in polypropylene or PVDF: centrifugal transfer of acids, caustics and plating solutions

01

Polypropylene or PVDF wetted ends: temperature ceilings and pH limits

Finish Thompson lists the same maximum temperatures for its sealless DB series and its mechanically sealed GP series: 180 °F (82 °C) in polypropylene and 220 °F (104 °C) in PVDF. [1] [3] Arkema, the maker of Kynar PVDF, gives as a guideline at ambient temperature a resistance limit of pH 12 for its PVDF homopolymers and pH 13.5 for its Kynar Flex copolymers, and names hot-acid applications among the uses of the resin. [5]

Arkema lists factors that change chemical resistance: exposure time, concentration, extreme temperature and pressure, temperature and pressure cycling, abrasive particles and the type of mechanical stress, and warns that certain combinations of chemical exposure and mechanical load can induce stress cracking. It recommends trial installations under actual service conditions, noting that immersion tests in individual chemicals do not predict behaviour when chemicals react exothermically together. [5]

The plastic body is only part of the wetted path. On Finish Thompson's DB11 the buyer also chooses O-rings in FKM, EPDM, Simriz or Kalrez, bushings in carbon, PTFE, ceramic or SiC, and shafts in ceramic or Hastelloy; its GP series offers bellows, multi-spring or double seals mounted externally. [2] [3] Editorial note: a strong caustic near or above pH 12 is the case to ask whether the PVDF offered is a homopolymer or a copolymer grade, and to check every elastomer against the same solution and temperature.

Give the supplier each solution's chemical names, concentrations, pH, temperature range and any solids, and ask for a compatibility statement covering the casing plastic, O-rings, bushings, shaft and seal faces.

02

Dense solutions: specific gravity, motor power and working pressure

The Department of Energy and Hydraulic Institute sourcebook Improving Pumping System Performance gives fluid power in horsepower as head (ft) × flow (gpm) × specific gravity ÷ 3,960, and notes that specific gravity affects the energy required to lift and move the fluid and must be considered when determining pump power requirements. [6]

Finish Thompson states the DB11's power range as 0.28 to 1.74 hp and 0.37 to 1.38 kW, both based on a specific gravity of 1.0; the two figures are listed against 3,450 and 2,900 rpm columns and do not convert into each other, so confirm which applies to your supply frequency. [2] For the GP series it lists maximum suction pressure of 15 psi (1 bar) with a bellows seal and 65 psi (4.5 bar) with a multi-spring seal. [3]

Editorial calculation with the DOE formula: 50 gpm against 50 ft of head needs 50 × 50 × 1.0 ÷ 3,960 = 0.63 hp of fluid power for water, and 1.14 hp for a solution of specific gravity 1.8 at the same flow and head. Applied to the DB11's 1.74 hp upper figure at specific gravity 1.0, the same head and flow at 1.8 would need about 3.1 hp, before efficiency changes. [6] [2]

State the solution's specific gravity and viscosity at operating temperature with flow and head, so the supplier sizes the motor and, for magnetic-drive pumps, the magnet coupling for the actual density.

03

Send the solution chemistry, the duty point and the density

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Solution: [chemicals; concentration; pH; solids]
Temperature: [minimum; maximum; cleaning]
Duty point: [flow; head; suction conditions]
Density: [specific gravity; viscosity at temperature]
Design: [sealed or magnetic drive; dry-running protection]
Materials: [PP or PVDF; O-rings; bushings; shaft; seal]
Motor: [voltage; frequency; enclosure]

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