Ensuring accurate vessel pressure control can be crucial for process quality. To achieve this, optimising valve response time is key, which means that integrated, sterilisation-in-place-capable systems can have an important advantage

Damien Moran at Bürkert Fluid Control Systems

In pharmaceutical and biotechnology manufacturing, accurate vessel pressure control is critical to maintain robust process standards and ensure repeatability across batches. This means effectively managing the headspace of air, nitrogen, CO2 and other neutral gases above the liquid, closely controlling the pressure, whether that’s during filling or emptying, or maintaining a constant set point.

While failure to accurately control pressure can result in fluctuations that impact product quality and consistency, it can also reduce throughput, with slower or less consistent filling and emptying rates reducing overall process efficiency. In the long term, excess or insufficient pressure can also stress the integrity of the vessel and connected hardware, leading to early maintenance challenges and unnecessary cost.

The immediate challenge of relying on manually controlled valves to manage vessel pressure, which can still be found on older systems or vessels outside of comprehensive traceability requirements, is that they are not responsive to dynamic changes. Even when maintaining a constant pressure within the vessel, the reliance on monitoring pressure sensors to identify deviations means a lag in response, the implications of which depend on the process and media involved. Meanwhile, manually managing pressure during vessel

filling or emptying highlights the reliance on skilled and experienced personnel. Ultimately, manually controlled valves are blind and unable to provide visibility on how they are performing, including whether deviations to the set point are subtle gradations or spikes.

In addition to enhancing control performance and reducing the reliance on human resources, automating vessel pressure control adds process visibility and traceability, enabling pressure data to be monitored, recorded, and analysed to optimise process efficiency and improve repeatability. The value of data analysis also extends to diagnostics, providing information such as valve opening times. This not only informs preventative maintenance to enable improved planning but also minimises the potential of unexpected downtime. If a vessel already integrates automated pressure control, the typical approach is to use a conventional tank pressure controller with multiple valves and sensors, in communication with a programmable logic controller (PLC). However, separate components, each of which has a varying level of performance and response time according to its assigned role, create a time lag and need to be integrated together. Moreover, this delay can also be exacerbated as the system resolves communications integration challenges. The result is that the control system delays can impact the process before the system can react.

Alternatively, a decentralised approach that integrates two control valves, one each on the inlet and exhaust of the vessel, plus a pressure sensor, creates a local, closed loop architecture that can be up to ten times faster in its response. Instead of sending signals back to a centralised control device, with communications slowed by third-party device integration, a decentralised vessel pressure control system can reduce communication time to just 200ms (milliseconds). This achieves greater precision and repeatability in pressure control, which can significantly improve the management of the process.

A reason that centralised pressure-control systems have been deployed on vessels, despite their potentially slower response, results from restrictions in hygienic design. Conventional control valves unsuitable for installation within the hygienic boundary means that pressure control will be located outside the vessel’s sterilised area. However, sterilisation-in-place (SIP)-capable control valves allow the control element to be positioned directly at the vessel’s inlet/ outlet, enabling a faster response to dynamic pressure changes. The leading choice in SIP-capable pressure control involves a control valve and pressure sensor integrated as a single block, machined from stainless steel to achieve a finish that optimises hygiene and enables use in aseptic processes, including a PTFE bellow. This design also enables clean-in-place (CIP) processes, with vertical parallel mounting of the inlet and exhaust valves enabling cleaning fluid to flow from top to bottom, with a self-draining system that removes dead legs to prevent contamination risks.

While it’s possible to achieve localised pressure control using separate hygienic control valves and pressure sensors, conventional proportional valves including CIP-rated designs face accelerated wear over time. If left unchecked, a degraded valve can also result in unpredictable valve operation and negatively impact the performance of the overall process. Instead, a pre-engineered, integrated SIP/CIP solution can add durability and minimise maintenance requirements. Stainless steel construction with an electropolished surface optimises resilience to corrosion, while a self-draining design also prevents retention of cleaning media and moisture to minimise component wear.

When integrating an automated pressure control system involving separate control valves and pressure sensors, this requires multiple components to work together as a coordinated control loop. This approach increases system complexity and the potential for integration and validation challenges throughout installation and commissioning, particularly if two or more third-party equipment manufacturers are involved. Not only does this add the potential of risk during commissioning, but later down the line, maintenance challenges can also present as a result of issues in device integration. Alternatively, a purpose-designed pressure-control solution that combines sensing and control functions, simplifies installation and removes the prospect of compatibility challenges. Instead, a single system only requires connectivity to the main PLC while providing responsive control within the SIP envelope.

Combining system components into a single unit that can be installed on the vessel’s inlet/outlet also reduces the process footprint. This approach removes the space required for the additional pipework and connections associated with pressure control systems that are mounted remotely from the vessel.

However, even with this existing architecture, integrated pressure control systems can be retrofitted to virtually any existing vessel, supporting a range of flow values. Meanwhile, for new installations, reducing the pipework and connections by locating the pressure control system on the head of the vessel can also decrease the overall hardware cost.

A further advantage of integrating a pre-engineered system with the support of a flow control specialist is the time-saving in specification. Engineering assistance not only takes away the complexity, but also ensures the system is optimally sized. Accurately defining requirements from the outset is key, including calculating factors such as KVs values and inlet pressures, and the scale of this challenge increases in line with the size and complexity of the overall system. While some design margin is necessary to accommodate variations in operating conditions, imprecise calculations can result in unnecessarily oversized, higher-cost valves that can compromise precise control and increase maintenance requirements. Alternatively, partnering with a flow engineering specialist helps to ensure the optimum specification and design. This enables a smooth, predictable integration, essential for maintaining project timescales, and it’s also more likely to result in reliable and efficient performance when the system is operational.

If an automated vessel pressure control system is already in place but installed outside of the SIP envelope, upgrading to an integrated, SIP-capable system located on the head of the vessel can enhance response times and improve pressure control performance. Not only can this improve process standards and repeatability, but a robust design can also reduce operational expenditure by minimising maintenance requirements and downtime. Thanks to the reduction in pipework, this upgrade also has the potential to reduce the total cost as well.

Alternatively, if a manual approach to vessel pressure management is still relied on, the advantages of automation will not only enhance process performance and efficiency, but it can also make managing the system significantly easier.

Damien Moran is regional business development manager, pharma & biotech, for North Europe at Bürkert Fluid Control Systems. Over his ten years with Bürkert, he has held business development and account management roles across the UK, Ireland and Northern Europe, supporting a wide range of customers and projects in the pharmaceutical and biotechnology industries. Before joining Bürkert, Damien worked in technical sales for process measurement and control equipment, giving him a wealth of experience in industrial fluid control and instrumentation. He holds an Engineering degree in Mechatronic Engineering from Dublin City University, Ireland.