In steam systems for pharmaceutical manufacturing, the “dryness fraction” and “pressure stability” of the steam used for sterilization and heating have a major impact on quality. To put the conclusion first, achieving reliable sterilization at the targeted temperature and time requires properly discharging the condensate (drain) that accumulates inside the piping, while also stabilizing the operating pressure with a pressure reducing valve. If drain remains, the steam becomes wet, which can contribute to poor heat transfer, water hammer, and corrosion, and may compromise the reproducibility of sterilization conditions. This article organizes drain countermeasures and the role of pressure reducing valves from a practical standpoint.
Key Points of This Article
- For pharmaceutical steam, “dryness fraction” and “pressure stability” are the keys to quality
- Retained drain tends to lead to poor heat transfer, water hammer, corrosion, and disrupted sterilization conditions
- The pressure reducing valve stabilizes the operating pressure and supports the reproducibility of sterilization temperature
Why Drain and Pressure Matter in Pharmaceutical Manufacturing
In steam sterilization (such as autoclaves and steam sterilization of piping), the temperature and pressure of saturated steam generally have a corresponding relationship, so obtaining the target temperature requires a stable supply of the corresponding pressure. If the pressure fluctuates, the temperature also wavers, which becomes a factor in undermining the reproducibility of sterilization conditions (temperature and time).
How Drain Affects Quality
Inside piping and equipment, part of the steam condenses due to heat loss, producing drain. When drain is retained, the steam becomes wet, and the drop in dryness fraction tends to leave the actual heat transfer insufficient relative to the apparent temperature. In addition, high-velocity steam pushing the drain along can cause water hammer, which may lead to damage to piping and valves. Retained water can also be a source of corrosion and fouling, so frequent discharge is required.
The Role of the Pressure Reducing Valve
Supply steam in a plant is often delivered at a relatively high pressure, and each piece of equipment uses it after reducing the pressure to match its operating conditions. A pressure reducing valve works to keep the secondary-side pressure near the set value even when the primary-side pressure fluctuates, thereby contributing to the stability of the sterilization temperature. In pharmaceutical applications, the selection of wetted-part materials and seal specifications also becomes a consideration, depending on the steam cleanliness requirements (the so-called clean steam / pure steam domain). Because the suitable specifications differ according to the required cleanliness classification, it is important to organize the conditions before making a selection.
Points to Keep in Mind for Selection and Design
It is common to combine a strainer, drain outlet, and, if necessary, a safety valve upstream and downstream of the pressure reducing valve. Because control tends to become unstable if the minimum flow rate is too small, it is essential to check the operating range including not only the maximum flow rate but also the minimum flow rate. Furthermore, when you want to suppress pressure and temperature fluctuations on the secondary side, examining the entire system—including the piping size and the placement of drain discharge points—serves as a guide for stable operation. Since the figures vary with the operating conditions, please regard this only as a general way of thinking.
Frequently Asked Questions
Q1. Why are drain countermeasures important in steam sterilization?
A1. It is because retained drain makes the steam wet, and the drop in dryness fraction tends to cause poor heat transfer. It can also affect the reproducibility of sterilization conditions. Proper discharge allows stable heating to be expected.
Q2. Does installing a pressure reducing valve stabilize quality?
A2. It works to suppress pressure fluctuations on the primary side and keep the secondary side near the set value. Since pressure and temperature correspond in saturated steam, it contributes to temperature stability. However, the design of the entire system is also important.
Q3. Should the minimum flow rate be checked when selecting a pressure reducing valve?
A3. Yes, checking not only the maximum flow rate but also the minimum flow rate is advisable. This is because control tends to become unstable if the minimum flow rate is too small. We recommend making a selection after organizing the operating range.
Q4. Is a pressure reducing valve for clean steam applications different from a standard one?
A4. Depending on the required cleanliness, examination of the wetted-part materials and seal specifications may be necessary. Suitable specifications differ by application classification. Please organize your conditions and consult with us.
Q5. How can water hammer be prevented?
A5. A discharge design that does not allow drain to be retained is fundamental. Reviewing the piping slope and the position of drain outlets can be effective in some cases. Examining the entire system serves as a guide for reducing water hammer.
Q6. Does the sterilization temperature also change when the pressure is lowered?
A6. In saturated steam, the temperature changes according to the pressure. Therefore, the setting of the operating pressure is closely related to the sterilization temperature. It is common to design by back-calculating the required pressure from the target temperature.
Q7. What should I do if I want to replace an existing pressure reducing valve with an equivalent product?
A7. Confirmation of specifications such as bore size, pressure conditions, flow rate range, and materials is necessary. Having nameplate information or drawings makes selection smoother. Organizing the information before consulting with us makes it easier to provide an appropriate proposal.
Summary
In steam systems for pharmaceutical manufacturing, a discharge design that prevents drain retention and pressure stability provided by a pressure reducing valve support the reproducibility of quality. Examining the entire system is also effective in reducing the risks of poor heat transfer, water hammer, and corrosion.
If you have concerns such as “I can’t judge whether the bore size is appropriate,” “I know the maximum flow rate but not the minimum flow rate,” “I want to select an equivalent for an existing valve,” or “I want to know the specifications suited to clean steam applications,” please feel free to send Yoshitake your technical and selection inquiries. After organizing your operating conditions, we will consider the suitable specification selection together with you.