Steiner Pumps – Stainless steel diaphragm pump (MK Stainless steel)

The MK series stainless steel diaphragm pump is an air-operated double-diaphragm pump with a wetted part made of SS304, SS316 or SS316L stainless steel. It is compressed air-driven, self-priming, dry-running resistant and has no rotating seals. The stainless steel version is available in five sizes: MK 15/20, 25, 40, 50 and 80. General information on the series and article coding can be found on the page Steiner Pumps.

Where is a stainless steel diaphragm pump used?

Stainless steel is chosen where corrosion resistance is important in combination with the possibility of regular washing and sanitising.

Typical media: syrups, concentrates, pastes, tomato paste, peanut butter, meat sauces, jams, applesauce, chocolate, molasses, food flavourings, alcohol-containing solutions, active pharmaceutical ingredients, emulsions, creams, perfumery compositions, disinfectants and detergents.

The design itself is suitable for sensitive products: there is no impeller in the pump, so shear is low and the product structure is not destroyed. Pastes, purées and emulsions pass through the pump without homogenisation.

The physical construction is selected for the specific product. Compliance with industry standards and accompanying documents are agreed upon per project — send your production requirements, and we will confirm which construction corresponds to them.

Five standard sizes: technical specifications

Head and air pressure are different quantities: 8.4 bar refers to the inlet air pressure, whilst 84 m refers to the liquid delivery head. The figures are based on tests carried out with water at 20 °C.

Threaded connections: BSP or NPT. Support foot with holes for anchor fastenings; on the MK 80 model, there are eight M16 bolts.

Stainless steel diaphragm pump: SS304, SS316 or SS316L?

SS304 — standard stainless steel version. Suitable for most foodstuffs, water, alcohol-based solutions and cleaning agents.

SS316 — additionally alloyed with molybdenum. More resistant to chlorides and to environments with increased corrosiveness. This is the choice for brines, acidic products, and processes using aggressive CIP chemicals.

SS316L — the same low-carbon steel. Less susceptible to intergranular corrosion in welded areas; used where the requirements for welded joints are the most stringent.

The central unit is made of polypropylene (for MK 15/20) or of polypropylene, aluminium or stainless steel (for MK 25 and larger models). The central unit does not come into contact with the product.

Diaphragms, balls and valve seats

The housing is made of stainless steel, but the elastomers that come into contact with the product are selected individually — it is these that determine the chemical and temperature limits.

Membrane. Santoprene, Hytrel, PTFE (Teflon), Viton (FKM), EPDM, Buna-N.

For food and pharmaceutical environments, the default choice is PTFE or EPDM; for hot CIP cleaning, the temperature limit is set precisely by the diaphragm.

Valve ball. For MK 15/20 — PTFE, stainless steel, Santoprene. For MK 25 and larger — Santoprene, Hytrel, PTFE, Viton, stainless steel, ceramic.

Valve seat. For MK 15/20 — SS304, SS316, SS316L. For MK 25 and above — Santoprene, Hytrel, PTFE, Viton, stainless steel.

Cleaning, maintenance and replacement of the membrane

The pump can be dismantled at the four-bolt joints without the need for special tools and without having to remove it from the pipework during the preceding operations.

The air valve has a modular design — it is serviced directly at the point of use.

The diaphragm has a central O-ring seal and a solid backing plate with an integrated metal element. Replacing the diaphragm is a routine procedure; it is the diaphragm, balls and seats that are consumable parts, whilst the body does not wear out.

The pump can withstand dry running, so purging the line with air after a product change does not damage the equipment.

Working with flammable liquids

The pump does not require an electrical supply — it is driven by compressed air. This is a fundamental requirement for working with alcohol-based solutions, solvents and other flammable substances.

For such applications, the product code is available in a conductive version (special code C) — it dissipates static charge.

ATEX explosion protection marking is documented when ordering for a specific zone and category of facility.

Frequently asked questions about stainless steel diaphragm pumps

What grades of steel are available?
SS304, SS316 and SS316L — for all five sizes of the stainless steel version.

What is the maximum capacity?
1,060 l/min (63.6 m³/h) — MK 80 with 3-inch connections. The smallest stainless-steel pump, the MK 15/20, delivers up to 57 l/min.

Is 8.4 bar the discharge pressure?
No, that is the maximum inlet pressure of the compressed air. The delivery head is up to 84 m.

Does the pump damage the product structure?
The design does not include an impeller, so the head is low. The pump is used for pastes, purées, emulsions and creams.

Is there a stainless steel version available for the smallest size?
No. The MK 06/10 is only available in polymer materials — PP, PVDF and POM. The smallest stainless steel model is the MK 15/20.

What is the maximum size of solid particles that can pass through?
From 2.5 mm (MK 15/20) to 9.4 mm (MK 80).

Does the pump withstand dry running?
Yes. There are no dynamic seals in the design, and operating the pump without fluid will not damage it.

Which membrane should you choose for food production?
Usually PTFE or EPDM. The final choice depends on the product, the temperature and the chemistry of the cleaning solution.

Are there any documents relating to food or pharmaceutical manufacturing?
The physical design and supporting documentation are tailored to the specific project and production requirements.

What is needed for the selection?
The product and its properties (viscosity, density, abrasiveness, solids content), product and wash water temperature, CIP chemistry, required flow rate, lift height and pipeline length, available compressed air pressure and flow rate, and requirements for materials and documentation.