Dosage Line Tubing

The selection of the correct tubing - in terms of material and size - is essential to ensure safe and trouble free operation. When considering which tubing to select, the following factors are important.

Material

• The material of construction of the tubing must be compatible with the chemical being dosed.
• Certain chemicals are naturally extremely aggressive; others can react just with specific materials.
• What ever the reason, some chemicals can cause some materials to pinhole or crack or become brittle - all of which ultimately result in failure of the dosage line.
• If a dosage line does fail, the implications can be extremely serious.
• Leaking chemical can cause corrosion or other damage to equipment or areas it leaks on to.
• Some chemicals can fume leading to a hazardous environment.
• Some chemicals are very dangerous to handle so leakages onto skin can cause irritation and/or burns.
• If leakage is under pressure, then sprays can occur which can be particularly dangerous if no protective clothing - particularly eye protection - is worn.
• Thus, always ensure that the material selected is suitable for the chemical(s) in use.

Pressure

• All materials have a pressure rating. If the pump in use exceeds this pressure rating then there is obviously a risk of causing tubing to fail.

Size

• Tubing size is normally denoted by the Interior Diameter (ID) and the Outside Diameter (OD).
• The tubing ends will normally terminate at the pump onto the delivery valve and the injection fitting.
• These two valves will be constructed to accept a certain size of tubing and the method of securing the tubing will usually be some kind of nut screwing onto an olive or taper arrangement.
• If the tubing size does not exactly match the valve size, it can become impossible to achieve a totally secure seal and hence leakage of chemical will occur.
• Sizes available are either Imperial - e.g.¼" x ½" or Metric - e.g. 4mm x 6mm.
• Our standard range of PULSAtron and PULSAtron Plus pumps has Imperial fittings. Metric fittings are available as an optional extra but it is obviously important to ascertain exactly the pump connection sizes in all applications.

Colour

• Most plastic tubing tends to be translucent which means that some light will be transmitted to the chemical.
• For certain chemicals this can cause a problem.
• Oxidising chemicals such as chlorine, hypochlorite, bromine etc can form small bubbles of oxygen when subjected to light. These "gas" bubbles can cause "gassing" which is when the bubbles collect in parts of the dosage pump head or lines.
• Gassing causes the pump to malfunction whereby chemical is either dosed at the incorrect rate or not at all.
• In these instances black - or a colour that does not transmit light -should be employed to reduce the risk of gassing occurring.

Delivery Line Route

• The distance and route between the dosage pump delivery valve and the injection fitting should be as short and as direct as possible and preferably vertical from the injection fitting.
• Long lines or tortuous routes should be avoided for the following reasons.
• They can cause the dosage pump to perform erratically due to pressure losses in the delivery line.
• Siphoning of chemical can occur back through the dosage pump into the tank leading to loss of chemical in the dosage line. In this instance, when the dosage pump is actuated, it can just fill up the line again without any chemical getting into the system being dosed.
• The more line there is, the greater the risk of it getting damaged.

Environment

• All dosage lines should be in an environment where they will not be subjected to freezing conditions. If this cannot be avoided, then frost protection must be employed.
• If chemical freezes in a line, the line can split leading to leakage after the thaw. Also the chemical itself can suffer degradation during freezing so that it is not able to provide the protection anticipated.

The types and sizes of tubing available are summarised in the table below.

Types of Tubing

Various types and sizes of tubing are available for different applications. If additional tubing is required other than the standard lengths supplied with PULSAtron and PULSAtron Plus pumps, ensure the correct choice is made.

Plastic

• Various types of plastic tubing are available for a multitude of applications.

Double Walled Plastic Tubing

• In some locations or applications, chemical leakage just cannot be contemplated at any time. Typically, when a dosage line goes through a highly sensitive process area or through a false ceiling over a highly populated commercial or retail area for example.
• For applications such as these, double walled tubing is available so that if the inner tubing does fail, the leak is contained within the outer tubing and transported to a less sensitive area.

Metal Tubing

• Usually small bore, typically 6mm or ¼" OD copper or stainless steel, for high temperature and/or high pressure applications.