Choosing instruments and connections for a sanitary metering skid comes down to two decisions made in order. The first is the measuring principle, driven by the product itself: whether it conducts electricity, how its viscosity and density change with temperature, whether it carries particles or entrained air, and whether the quantity is needed as mass or volume. The second is how the chosen device is built and installed: its hygienic design, process connection, seal material and mounting orientation on the skid, all judged against the cleaning regime. Skip the second decision and a meter that measures well can still become the hardest point in the line to clean.
The general architecture of a liquid metering skid, with meter, temperature and pressure measurement, control valves and a flow computer or controller on a common frame, is the same one used for fuels and chemicals. This page does not repeat it. It concentrates on what changes when the liquid is a food or beverage: hygiene, cleanability and the real scope of hygienic design certificates.
Matching the measuring principle to the product
Two principles dominate food liquid metering: electromagnetic (mag) flow meters and Coriolis mass flow meters. A mag meter has no moving parts and an unobstructed full-bore tube, but it only works above a minimum liquid conductivity, and that threshold depends on the model and line size, so the product's conductivity has to be checked against the manufacturer's limit. A Coriolis meter does not depend on conductivity, measures mass directly and also reports density. Where recipes, concentration or mass-based invoicing matter, that can decide the choice.
How product properties steer meter selection
Product property | Why it matters in design | Effect on selection |
Electrical conductivity | The magnetic principle relies on the liquid being conductive | For low-conductivity products, Coriolis or another principle is evaluated |
Viscosity and its temperature dependence | Drives pressure drop and pump sizing; product may thicken as it cools | Meter size, tube geometry and allowable pressure drop follow from it |
Particles, fibers or fruit pieces | Narrow passages can collect deposits or block | Full-bore or straight-tube designs are favored; complex internal geometry is questioned |
Entrained air or foam | Volumetric meters may count air as product; two-phase flow degrades accuracy | Air elimination needs and meter behavior with gas are reviewed together |
Required quantity | Invoicing or batching may run on volume or on mass | Mass and density point to Coriolis; volume alone often suits a mag meter |
Cleaning and sterilization conditions | Meter and seals see detergents and hot water or steam | Wetted materials, seal type and electronics temperature limits are checked |
Sanitary connections and mounting orientation
A stainless meter body installed with ordinary flanged joints can still leave a gap where the gasket meets the product, and that gap becomes a pocket cleaning solution cannot reach. Meters built for hygienic service come with connections used in food plants, such as clamp fittings, hygienic threaded unions and aseptic flanges. The 3-A standards list includes separate standards for flow meters and for sanitary fittings; which connection is used in practice depends on the plant's existing tube standard and cleaning method.
Orientation matters as much as the device. Some single straight-tube Coriolis designs are described as self-draining, but that only works if the meter is installed at the angle the manufacturer specifies and in line with the overall slope of the skid piping. With mag meters, the tube must stay full and the electrodes must sit where air bubbles will not collect. Temperature sensors, sample valves and pressure taps should use short branches swept by the main flow; long blind connections are the hardest spots to clean.
What a device certificate does and does not cover
Hygienic meter datasheets often mention EHEDG or 3-A. These are device-level documents. EHEDG states that it typically certifies individual components rather than large, complex machines or processing systems, and each certificate lists the equipment type, sizes and the seal materials that were tested. The 3-A Symbol identifies equipment that meets a specific 3-A Sanitary Standard, and the models covered under each license are listed separately.
One Coriolis manufacturer's datasheet spells out that its 3-A and EHEDG status applies only with specific hygienic process connections and a specific housing option. Order the same meter with a different connection, or fit a gasket compound that is not on the certificate, and you may be outside its scope. More importantly, mounting several certified devices on one frame does not make the skid hygienic. Pipe slope, dead legs, branch connections and whether cleaning fluid reaches every wetted surface still have to be designed and then verified.
Records, traceability and food contact materials
In food plants, metering data does more than report a quantity. Logged together with batch number, product temperature, transfer time and confirmation that the last cleaning cycle completed, it becomes part of the traceability record. The EU framework regulation for food contact materials requires that materials do not transfer substances to food at levels that endanger health and that they are traceable, with additional rules for plastics. In the United States, polymers in repeat-use food contact articles fall under a separate part of the federal regulations. Declarations of compliance for gaskets, O-rings and any plastic parts should therefore be part of the supply documentation.
Where TLY Enerji contributes
TLY Enerji provides engineering support in selecting measurement technology from product and process data, and its product range includes Coriolis and electromagnetic flow meters. Depending on project scope, services can cover equipment supply, system integration, installation, testing and commissioning, as well as data acquisition on the PLC or SCADA side. This page makes no claim of food-industry experience; for hygienic applications, supply boundaries and documentation expectations are agreed project by project.
Data we need to size and select the meter
· Product name, conductivity, viscosity and density, and how they vary with temperature
· Presence of particles, fibers or entrained air
· Minimum and maximum product flow, plus the flow used during cleaning
· What the reading is used for: batching, inventory, internal transfer or invoicing
· Hygienic connection standard and tube sizes used on site
· Cleaning and, if applicable, sterilization conditions: chemicals, temperatures, durations
· Documents expected: hygienic design certificate, material and seal declarations of compliance
Related pages
· Stainless steel metering systems: Why choosing a stainless grade is a separate decision from hygienic design.
· CIP / SIP compatible systems: How meters and sensors cope with cleaning and sterilization cycles.
· Hygienic transfer systems: Pumps, valves and piping that feed the metering skid.
· Food-grade and sanitary liquid transfer facilities: Sector requirements and solution groups.
· Custody transfer truck loading skids: System-level approach when the reading is used for billing.
Questions about sanitary metering
Mag meter or Coriolis for milk or juice?
Both products usually have enough conductivity for a mag meter, but the value should still be checked against the manufacturer's threshold. If volume is all you need, a mag meter is simple and adds little pressure drop. If you need mass, density or concentration, or if the product carries variable amounts of air, a Coriolis meter tends to be the better fit. The final choice rests on product data and on how the reading will be used.
Does using an EHEDG or 3-A meter make the skid hygienic?
No. These certificates apply to the device and are usually limited to particular connection types, sizes and tested seal materials. A hygienic skid also needs correct pipe slope and drainage, no dead legs, well-placed sensor branches and proof that cleaning fluid reaches every surface. Those points are handled in the skid design and confirmed during commissioning.
Should the meter be installed horizontally or vertically?
It depends on the meter type and the manufacturer's installation instructions. Where self-draining is required, the meter is normally set at an angle that lets product run out by gravity. For mag meters, the priority is keeping the tube full and positioning electrodes where bubbles cannot collect. Orientation should be fixed before the skid layout is drawn.
Does the cleaning flow rate affect meter selection?
Yes. Cleaning solution is often circulated at a flow different from, and sometimes higher than, the product flow to keep the piping turbulent. The meter must handle that flow without excessive pressure drop, and if the cleaning flow is to be measured and recorded by the same meter, its range has to cover that value as well.
Why does the gasket material need separate attention?
The gasket touches both product and cleaning chemicals, and hygienic design certificates often apply only to the seal compounds that were tested. Food contact rules also call for declarations of compliance for elastomers and plastics. If a different gasket is chosen, both chemical resistance and certificate scope need to be rechecked.