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Neutralizing and pH control systems – FAQs

The answers to questions on this web page are aimed at readers who have at least elementary knowledge of pH and acid/base chemistry. If you don’t find the answers you need on this FAQ page, why not contact us directly with your questions? We will answer you in person and if the matter is of broad interest we will add your Q&A to this page.

Q: What is the difference between a pH Control System and a Neutralizing System?

A: “pH Control System” is the general term for equipment of this type whereas the term “Neutralizing System” indicates a pH Control System configured to bring the pH of treated liquid to a pH which is close to neutral.

Systems designed to bring the pH of treated liquid within a narrow pH band around 7.0 are generally referred to as Neutralizing Systems. A typical control band for a Neutralizing System is pH 6.0 to pH 9.0

Systems designed to bring pH to some specific value outside the neutral band are generally referred to as pH Control Systems.

Q: I don’t understand the difference between 1-way and 2-way pH Control Systems. What is a 1-way pH Control System?

A: If a pH Control System always has to change the pH of the treated liquid in the same direction, it is referred to as a 1-way pH Control System. Thus, if a chemical process liquid always has an initial pH = 8.0 and this liquid must always be adjusted to a higher pH (say pH = 10.0, for instance) the system needs to increase the pH. Most likely, in this case a 1-way pH Control System will be provided to add base and achieve the desired pH increase.

Similarly an example could be given to illustrate a 1-way pH Control System being used to add acid to a process liquid in order to reduce its pH to a lower value.

Q: Are there any physical differences between the 1-way models that add acid and the ones that add base?

A: ChemIndustrial designates its 1-way pH Control Systems as either “A” models (configured to inject acid) or “B” models (configured to inject base). The main difference between them is that “A” models feed concentrated acid and thus face generally tougher corrosion conditions. Because of this, certain parts of the “A” models are built from more corrosion resistant materials and are thus slightly more expensive than “B” models.

In addition to differences between the materials used in the “A” and “B” models, the instrumentation system has to be configured to recognize the necessary direction of pH change.

Q: What about 2-way systems?

A: These are needed when the required direction of pH correction can be either up or down. A very common situation that requires 2-way control is one where the pH of a process stream that needs treatment varies above and below the required final pH. In this case, the pH Control System must sometimes feed acid to reduce the pH of the process liquid and at other times it must feed base to raise the pH.