Filter basket 

pressure sensor

"I wonder why and how you measure the filter pressure."

"Let me tell you about the pressure inside the filter basket."

Q. Why is the filter basket pressure measured? 

A. The term "extraction pressure" may be defined as "pressure formed by a pump acting as a resistance to the force of pushing water out of the coffee pump when extracting the coffee pump". If the pump force is constant and the resistance of the coffee puck is constant, the extraction pressure is constant. If you can observe that the extraction pressure is constant, it will be an important indicator of extraction consistency.

Q. Is the pressure inside the filter basket known during extraction?

A. A small number of machines measure the exact extraction pressure by installing a pressure sensor at a position passing through the final orifice. However, much more machines measure 'pump pressure', which is not the same as 'filter basket pressure'.

Existing portafilter pressure gauges cannot extract coffee because the sensor is blocking the drain. Among the Portafilter-type sensors, the Belkafilter is the first to measure the pressure inside the filter without interfering with coffee extraction.

Q. How does the pressure inside the filter actually change during extraction?

A. During extraction, a pressure lower than 'pump pressure' is formed inside the filter, and the pressure varies depending on the cause of the change in puck resistance.

Q. How do I use the 'Filter Pressure Sensor' on the Belkafilter?

A. You can set extraction pressure criteria according to the barista recipe and quantitatively evaluate continuous extraction consistency.

By inserting a blind filter, you can check the actual pressure characteristics of the machine and continue to check that the pump performance is maintained.

TargetIndicatorTo check indicator
Managing extraction consistencyCoffee puck resistance change during extractionDuring coffee extraction, estimated by pressure changes inside the filter
Management of machine pressure performancePressure inside filter with no flow
Measure using 'blind filter', without coffee
Management of machine pressure performance
Pressure inside filter with constant flow
Measure using 'Orifice Pad™' without coffee

"Can you show me how to use it?"

"First, check the pump pressure of the machine you've been using."

Check the pressure the pump creates when pressurized by the machine with the 'blind filter' inserted without filling the coffee. The maximum pressure may remain constant, but it may increase gradually or occasionally decrease.

Repeat the same measurement several times to see how constant it is.

Now, remove the blind filter and insert the Orifice Pad™ developed by Belka. When the machine is running, a constant flow rate persists. You can see how much pressure there is, whether it stays constant, rises, falls.

Repeat the same measurement to see how constant it is.

If you're using a single pump machine, put an orifice pad in the Velcar filter and start the machine. Try operating another group at the same time. You can see how much pressure drop occurs. The size of the pressure drop may be very small, but it may be more than 1 bar depending on the structure or aging of the machine.

Again, repeat the same measurement to see how constant it is.

"You can manage machine performance like this."

By measuring and recording each group of the machine in the above way, you will be able to manage the aging of the pump by checking it regularly.

"Now, let's extract it as usual."

Try to extract as consistently as possible with a Velka filter as usual.

If your machine has a pre-infusion function, you can see how many bars the pre-infusion actually goes, and how gradual or rapid the pressure increase is.

During extraction, when the maximum pressure is reached, you can see how much the pressure is lower than when the blind filter is applied.

If the pressure is maintained or gradually decreased in the actual extraction compared to the pressure characteristics of my machine, this can be used to estimate the change in the puck resistance. (The extraction pressure graph does not correspond 1:1 to the change in the puck resistance. It is recommended to consider the change in flow rate together.)

If the same extraction pressure graph is consistently reproduced in the same test several times, it will be possible to view it as a pressure criterion for that extraction and determine the pressure consistency in the subsequent extraction.

"Please check the accuracy."

Q. How do you measure the pressure without blocking the flow of coffee?

A. When pressure is applied to the filter basket, the basket is slightly stretched, although invisible. We developed a completely new sensor structure using this phenomenon. The sensor is outside the filter basket, so there is no hole in the filter basket, and coffee is not touching the sensor.

Q. It measures pressure in a new way, is it less accurate?

A. We did a lot of tests, and the results didn't make much difference. I'll show you the data.