Net-weight filling head for rotary bottle fillers: a filling valve that closes on the reading of a load cell under each bottle
Net-weight filling valve on a rotary filler · one load cell under each bottle, OIML R 61 accuracy classes, sigma below 0.5–1 g at 1 litre, and where weighing errors come from
On a weight filler each station on the carousel has its own filling valve and its own load cell carrying the bottle plate. The scale is zeroed with the empty bottle, the valve opens, and the controller closes it when the bottle has gained the target net mass, so the dose is measured as it goes in rather than checked afterwards. This page is about that pairing of valve and load cell, and what accuracy it is held to: the legal-metrology classes for automatic gravimetric fillers, the sigma values filler makers publish, and the error sources between the load cell signal and the valve closing.
Filling heads (valve, nozzle and per-station load cell) on rotary net-weight fillers for still liquids in bottles and jars: edible oil, sauces, household chemicals, lubricants and similar. Counter-pressure valves for carbonated drinks and flowmeter-controlled valves are covered on the Beverage filling nozzle assembly for bottle and can fillers page; filling heads and lances for drums, pails and chemical containers on the Filling head for drum and container filling of chemical liquids page; drum-filling scales on the Weighing platform for drum filling page; pulp and fruit-piece valves on the Hot-fill valve for pulpy juices page; aseptic valves on the Aseptic filling valve page.
CNFX editorial research · Sources checked October 13, 2026 · 4 sources
OIML R 61 classes for a weigh-filling station: 12 g per fill at 500–1000 g in class X(1), scaled by the class factor
A rotary weigh filler is an automatic gravimetric filling instrument (AGFI) in OIML terms. R 61-1:2017 makes the manufacturer state an accuracy class X(x) and limits how far each fill in a test may deviate from the average of all fills, the maximum permissible deviation (mpd). The Table 2 values below are for class X(1); for another class they are multiplied by the class factor x, which must be no more than 2 and of the form 1, 2 or 5 × 10^k. [1]
The same recommendation limits the gap between the preset value and the average fill to 0.25 of the in-service mpd, and requires a rated minimum fill (Minfill) below which the limits do not apply. With a scale interval d of 1 g, Table 3 sets the smallest permissible Minfill at 111 g for class X(0.2), 22 g for X(0.5), 11 g for X(1) and 6 g for X(2). [1]
Editorial calculation: for a fill in the 500–1000 g band, such as 1 L of water (taking 1 L ≈ 1 000 g), class X(1) allows 12 g at initial verification; X(0.5) allows 0.5 × 12 = 6 g and X(0.2) allows 0.2 × 12 = 2.4 g.
Fill mass F
mpd for X(1), initial verification
mpd for X(1), in service
F ≤ 50 g
7.2 % of F
9 % of F
100 g < F ≤ 200 g
3.6 % of F
4.5 % of F
300 g < F ≤ 500 g
2.4 % of F
3 % of F
500 g < F ≤ 1 000 g
12 g
15 g
1 000 g < F ≤ 10 000 g
1.2 % of F
1.5 % of F
F > 15 000 g
0.8 % of F
1 % of F
Ask the supplier for the accuracy class X(x) and reference class Ref(x) marked on the filler, its Minfill and scale interval d, and whether the machine is supplied with OIML or national pattern approval for the fill sizes you will run.
02
Sigma below 0.5 g and about 1 g at one litre: what weigh-filler makers publish, and the four error sources between load cell and valve
Filler makers state repeatability as a standard deviation at a named fill size rather than as an OIML class, so the two need putting on the same footing before comparing heads.
Serac describes the net-weight control as adjusting itself for changes in aeration, temperature or viscosity of the product, and lists edible oil, detergents, cosmetics, sauces and automotive products among its applications. [3]
Yun Xu and Xue Meng Xu, studying weight filling of edible oil, trace the error of a weight filling system to four causes: load cell error, the operating time delay of the filling valve, PLC response delay, and the shock of the liquid stream on the bottle. [4] The last three all act between the moment the target weight is read and the moment flow actually stops, so they are properties of the valve and its control as much as of the scale.
Editorial calculation: if fills follow a Gaussian distribution, about 99.7 % fall within ±3 sigma; sigma < 0.5 g gives a spread under ±1.5 g, and 1 g sigma about ±3 g, both inside the 6 g mpd of class X(0.5) for a 1 kg fill. This is a comparison aid only; the OIML test uses the deviation of each fill from the average over a defined number of fills, not a sigma.
Filler
Published accuracy and range
Source
Hema ACCES (Synerlink, Barry-Wehmiller), edible oil
Sigma < 0.5 g for 1 L; 80–5,000 ml without changing nozzles via a patented double flap valve; 15–66 filling heads; up to 40,000 bottles/h; EHEDG-certified IP69K load cell; non-contact valves [2]
Maker product page
Serac RB, rotary weigh filler-capper
Accuracy of about 1 g per litre (1 sigma standard deviation), which Serac says “can be expected”; containers 100 g to 60 kg; up to 42,000 containers/h at 1 L; OIML certification offered as an option [3]
Maker product page
Ask for sigma at your fill size, on your product and bottle, with the number of fills measured, and for how the head handles valve closing delay (pre-act or in-flight correction).
03
Valve, nozzle and load cell at one station: what to fix in the order
Part of the head
What the sources say
Fix in the order
Load cell under the bottle plate
Hema specifies an EHEDG-certified, IP69K load cell [2]; R 61 requires a stated scale interval d and Minfill [1]
Cell rating, washdown protection, d
Filling valve
Valve operating delay is one of the four error sources [4]; Hema uses a double flap valve across 80–5,000 ml [2]
Valve type, closing time, coarse/fine stages
Nozzle
Hema's valves do not touch the bottle [2]; Serac offers multiflow nozzles for foamy products [3]
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Product: [liquid; density; viscosity; foaming; temperature]
Containers: [material; volume range; neck size]
Fill: [target net mass; smallest and largest fill]
Accuracy: [OIML R 61 class X(x); sigma required at fill size]
Output: [bottles/h; number of heads]
Hygiene: [washdown rating of load cells; CIP]
Approval: [OIML or national pattern approval needed]
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Share this page
Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
What accuracy does OIML R 61 require of a weigh filler?
For class X(1), each fill of 500–1000 g may deviate up to 12 g from the average at initial verification and 15 g in service; other classes scale these values by the class factor. [1]
How accurate are rotary net-weight fillers in practice?
Synerlink quotes sigma below 0.5 g for 1 L on its Hema ACCES edible-oil filler; Serac says about 1 g per litre (1 sigma) can be expected on its RB filler. [2][3]
Where does weight-filling error come from?
Yun Xu and Xue Meng Xu list load cell error, filling valve delay, PLC response delay and the shock of the liquid stream. [4]
Sources and what still needs a direct check
Sources checked 2026-10-13. Class limits come from OIML R 61-1:2017, the international recommendation for automatic gravimetric filling instruments; published sigma and ranges from the Hema (Synerlink) and Serac product pages; error sources from Yun Xu and Xue Meng Xu's edible-oil weight-filling paper (abstract).
