How to... Apply pressure siphons

OC Verhulst air treatment units have a variety of condensation drains. These drains must be fitted with the negative or positive pressure siphons supplied.

Positive or negative pressure siphons. What they are, how to fit them and what to watch out for during maintenance. To find out all about them, see the text below or watch the instruction video's. 

Positive and negative pressure

Siphons are normally fitted to the bottom of the unit. Their purpose is to drain off excess water in the form of condensation from a chiller or humidifier. They prevent leakage of air through the condensation drain in the air treatment unit. Positive and negative pressure siphons are available. The negative pressure siphons have is a removable top that contains a diaphragm. The positive pressure siphon can be recognised by the swan-neck trap.

The negative pressure siphons are always found in the air intake section in the treatment unit in front off the fan. Positive pressure siphons are situated in the blow-off section, after the fan.


There is a summary of the OC Verhulst siphons available in the PDF file below (Dutch). The videos below show you exactly what to do when fitting the screw-type or glue-in siphon.

Siphon maintenance

Siphons should be included in the preventative maintenance of the air treatment units (to do this, turn the unit off). Check the seals for any leaks check whether there is enough water in the swan-neck trap and when necessary, clean the siphons. Negative pressure siphons can be unscrewed and all the individual parts washed in clean water. After a long period of not being used, the positive pressure siphon must be refilled with water.

When refitting, ensure that the one-way valve is fitted correctly.

Fitting the siphon

Refer to the instruction video for the correct fitting of the glue-in siphon.

View the instruction video for the correct fitting of the screw-type siphon.

Make sure that the siphon is fitted in the right place (positive of negative pressure). Position the siphon vertically. Screw it in securely or apply PVC glue. The positive pressure siphon must be filled with water before the air treatment unit is turned on.

A siphon must be fitted to every condensation drain. It must not be connected to several drains.

Do not connect a negative pressure siphon directly to the drains to the sewer. It must be connected to the drains to the sewer so that there is no pressure. If the unit is mounted outside, the condensation can be drained on the roof/in the gutter. If the air treatment unit is in an environment prone to frost, ensure that the siphon has frost protection.

If you are unsure whether you should carry out maintenance or order a replacement siphon, please get in touch with the Renovation and Maintenance department of your Orange Climate dealer.

Download als PDF

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