Your pressure relief valves are the best insurance you have against safety incidents in your plants and along your pipelines. We get a lot of questions from customers about how to select and operate pressure relief valves. Here are answers to three of the most common questions we hear.
Can I reset the pressure on my pressure relief valve?
Yes. Pressure relief valves can be reset and VR stamped with full inspection by an authorized valve repair company. Some repairs may be necessary before the valve can be reset. For example, the valve may need a spring change.
Warning: PRVs should NOT be reset above the maximum allowable set pressure of the valve. We’ve seen this happen, and it presents a major safety risk. Before resetting the pressure on a valve, make sure that the pressure you want is within the allowable set pressure for the manufacturer’s valve series.
I’m operating close to the set point on my valve. How can I keep it from simmering or lifting?
In general, the operating gap will vary depending on the system and valve type. Most pressure relief valves can be operated at up to 90% of the set point. Some metal-seated valves may get up to 94%, and some soft-seated valves over 101 psi can handle operating pressures up to 95% (for example, the Consolidated 1900 series with a soft seat can handle this higher pressure). If you exceed those thresholds, the valve will simmer. This can damage the valve and will more than likely lead to leakage and system downtime. Here are three things you can do to reduce simmer on your valves.
1. Lower your operating pressure
Many companies operate valves at higher pressures because they want to increase production. However, this often lead to the exact opposite result.
Here’s an example. Imagine a valve that opens at the tag pressure and has a 7% to 10% blowdown. That means the valve would blowdown to 90% of tag pressure. In other words, it would hold tight to 90%. If you were to operate that valve at 91% or 92%, you would push the valve into simmer and possibly actuate the valve with very little system fluctuation. This would more than likely cause valve leakage and valve damage, and increase your downtime.
Alternatively, if you were to operate the valve at 90%, rather than 91% or 92%, you would reduce the likelihood of pushing the valve into simmer or actuating the valve. This would, in turn, reduce the chances of valve leakage and damage, and decrease your downtime.
In other words, reducing your operating pressure can actually increase production, not reduce it.
2. Use a pilot-operated relief valve
In some situations, switching to a pilot-operated relief valve can allow you to operate at 95% to 98% of the set point.
3. Switch to a soft-seated valve
Particularly in areas with high vibration, a soft-seated valve will allow you to operate the valve at a higher pressure.
I need a new pressure relief valve. What information do I need to provide?
When replacing a pressure relief valve, it’s common for companies to just replace it with a valve with the same nameplate information. This may be fine if the valve was not causing a problem, but if the valve is a bad actor, it’s possible that it wasn’t the right valve for the application in the first place.
We recommend always verifying the sizing and selection of a replacement valve. Download a sizing sheet for steam, air, and liquid pressure relief valves.
Have a question about your pressure relief valves? Ask us!
Is your current dispense valve system giving you accurate deposits with minimal maintenance — or are you applying inconsistent amounts of fluid and wasting too much time and money on downtime, rework, and cleanup?
This blog series discusses common problems encountered with typical dispense valve systems by asking some of the most common questions. It also offers helpful tips for improving valve performance. This first part in the blog series answers the top two questions we have encountered most frequently. We hope that you find this information helpful.
In most situations, best results will be obtained with a valve style and configuration carefully matched to the specific properties of the fluid being dispensed.
Thick Fluids
Thick materials like RTV silicone or heavy grease, for example, pose very different challenges than thinner fluids like adhesives or threadlockers. When using thick fluids, a high-pressure valve with a balanced spool design will provide good control. Also, look for a snuff back feature as it will prevent drooling and tailing and help reduce the rework and cleanup often associated with these more challenging assembly materials.
Thin to Medium-Viscosity Fluids
Thin fluids like solvents and watery adhesives have much different requirements, especially when very small deposits are needed. For these applications, needle valves are often recommended because shutoff occurs close to the valve outlet or dispense tip. This is an important design feature because it minimizes dead volume that can cause dripping or oozing. For critical applications, there is even a needle valve that seats the needle in the dispense tip instead of the valve body. By virtually eliminating dead volume, this design makes it possible to produce even smaller and more consistent micro-deposits.
Learn more about how to choose the right valve by downloading our Dispense Valve Selection Guide.
Tricky Fluids Like Cyanoacrylates (CAs)
Wetted internal parts, as well as any fittings and tubing that come in contact with the fluid, should always be carefully chosen for compatibility with the fluid being dispensed. When working with cyanoacrylates, for example, wetted parts made of inert Ultra High Molecular Weight (UHMW) polymers are a good choice because they will not react with the fluid. Nylon or metal fluid fittings, however, should never be used with CAs because they absorb moisture and will promote premature curing. Use polyethylene or polypropylene fittings instead. Chemically inert, polyethylene-lined or PTFE FEP tubing are good choices for fluid feed lines.
Learn more about the right setup and maintenance for cyanoacrylate dispensing by downloading our Cyanoacrylate Dispensing Guide.
Taking a “system” approach to fluid dispensing and carefully evaluating all the details — even something as small as a fluid fitting — will help prevent many problems on your assembly line. A dispense valve system has four main components:
The greatest accuracy, reliability, and production yields will be obtained when all four components are engineered to work together as an integrated system. This approach will also simplify qualification and validation processes. Optimum PTFE-lined tips work best with low-viscosity cyanos. They feature a special lining that prevents curing and clogging.
A valve paired with a dedicated valve controller will typically provide faster response time than a valve triggered by mechanical means or a remote PLC. A dedicated controller will also allow deposit size to be fine-tuned with much greater precision than other methods and can be interfaced with the assembly line’s main PLC.
Precision dispense tips should be of high-quality materials to ensure unobstructed fluid flow and matched to the specific fluid and volume being dispensed. Fluid tanks should always be fitted with constant bleed regulators to maintain steady fluid pressure and prevent variations in deposit size as the fluid level moves from full to empty.
In the middle of coping with day-to-day production challenges, it can be difficult to calculate just how much poor valve performance is really costing you. However, doing so could save you money, increase production, reduce bottlenecks, and improve the overall quality of your products.
In the next part of our series, we’ll look at how to set up your valve system for optimal performance by providing answers to some troubleshooting questions.
Have a question about how to choose the right dispense valve system to begin with? Don’t hesitate to email us at info@nordsonefd.com.