For many years, break-pressure tanks were considered the only reliable way to create a complete pressure break in a pipeline. Advances in valve technology now offer alternatives. The Ratio Pressure Reducing Valve (RPRV) is one.
Each valve uses a piston designed to deliver a precise pressure-drop ratio. Compared with pilot-operated pressure-reducing valves, the RPRV has several major advantages:
- It is tamperproof, with no pilots or external controls
- It reacts instantaneously, which allows several valves to operate in series without instability
- It is inherently failsafe and continues operating even if the main seal or O-rings are damaged, producing only a minor leak
This makes them a good choice where simplicity and reliability are important. RPRVs have been used with great success in the underground mining industry for decades.Their wider use has lead to them being considered as a replacement for the traditional break-pressure tank. But, some tank manufacturers have raised concerns. We’ll address these below.
Reliability and Fail-Safe Behaviour
Some argue that the RPRV cannot be fail-proof because it contains soft components such as seals and O-rings. In practice, a damaged seal only results in a small, visible leak that signals the need for maintenance. The valve continues to operate normally, and a small downstream relief valve can be added if required. The RPRV does not have a failure mode that would cause it to stop functioning completely.
Performance in Dirty Water
Break-pressure tanks rely on components with fine orifices, which are prone to blockages. The RPRV, by contrast, has no fine orifices. Its main control element is robust and resists clogging, making it more reliable in poor-quality water.
Storage Requirements
Because the RPRV does not include built-in storage, some assume this is a disadvantage. In reality, it removes the risks associated with storage tanks: contamination, tampering, water theft and damage to level-control systems.If storage is needed, it can be provided separately.
Stability in Multi-Valve Installations
Unlike pilot-operated control valves, RPRVs do not hunt or compete with each other. Mining installations commonly use four or more RPRVs in series, and these systems remain stable under varying demand.
Turndown Capability
RPRVs can handle turndown ratios of up to 5:1. By comparison, level-control valves in a tank system are typically limited to around 4:1 before cavitation becomes a concern. And, the inlet valve on the tank always discharges to zero downstream pressure, which restricts its turndown capability even further.
Component Count
A common claim is that break-pressure tanks have fewer components. This is not true when compared with RPRVs. The RPRV has only one working part.
Material and Cost Considerations
Break-pressure tanks are often built using 3CR12 or 304 stainless steel for corrosion resistance. If needed, RPRVs can be manufactured from 316 stainless steel at significantly lower cost than a full tank installation.
Pressure Output
Break-pressure tanks reduce pressure to atmospheric levels, which often forces operators to install pumps to supply users located near the tank. An RPRV can be selected to deliver a suitable working pressure directly, removing the need for additional pumping in many cases.
