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Comment PDF Operations & Maintenance

How to Troubleshoot and Maintain Pressure Regulators

By Jonathan (Jon) Kestner |

Following a five-step process enables better outcomes for fluid system control

Most often, operators and technicians will interact with components like ball valves or needle valves when adjusting a system’s operation. However, just as important to the effectiveness of a system are the pressure regulators that work to deliver steady pressure, so these common valves can perform their function. Pressure regulators are complex fluid system components that require careful thought during system design, installation and operation to realize safe, trouble-free performance. A regulator’s main purpose is to maintain steady pressure in a fluid system application. However, a regulator’s ability to reliably perform that function can become compromised over time and may require investigation to determine if the regulator itself is the problem or if another system issue is to blame.

Issues such as the following are most commonly related to the regulator’s seat, diaphragm and poppet:

  • Pressure leakage across the seat when closed
  • Loss of pressure control
  • Fluid leakage to atmosphere

These issues do not necessarily mean the regulator needs to be replaced. The regulator can likely instead be maintained to prolong its life and reduce its total cost of ownership. In fact, maintenance is to be expected, as the Compressed Gas Association (CGA) notes that “regulators do not have infinite service life” in its pamphlet E-15-2017, “Guideline for Periodic Service Program for Industrial Gas Regulators, 3rd Edition.”

To properly troubleshoot a regulator’s performance, technicians can follow a five-step process that begins with testing the regulator, followed by inspection and a decision on whether to maintain, overhaul or replace it — based on assessments from the first two steps. We’ll review this process, along with exploring common issues associated with regulators, including causes and solutions, to help chemical plants, petroleum refineries and others in the chemical process industries (CPI) realize better outcomes from their fluid systems.


Pages from CHE_1118_DomesticHIRES


 

Step 1: Testing regulators

Testing a regulator is highly recommended — if not required — following regulator installation and maintenance to ensure accurate, as well as safe, operation. System operators should also test a regulator if they notice leaks, unexpected pressure increases or decreases, or any of the issues noted in the “Regulator Troubleshooting Tips” sidebar (above) and Table 1. Testing should be part of a facility’s preventive maintenance program, with regulators placed on inspection intervals based on their service environment and industry recommendations.

t1

To verify a regulator’s operation, maintenance technicians will typically perform two primary tests — a seat test and a shell test — to ensure the regulator isn’t leaking within the system or to atmosphere.

Seat leak test. To perform seat leak testing, a technician will conduct both a low-pressure and a high-pressure test to ensure the seat seals with the regulator poppet under both conditions and doesn’t allow pressure and system fluid to escape to the outlet side. Such leakage is known as creep, and can result from damage to the seat or from debris stuck between the regulator’s poppet (also called its main valve or control element) and seat. (See Figure 1 for a diagram of regulator components.) Since the shut-off force on a regulator seat is related to the inlet pressure, conducting both a low- and high-pressure test is important to ensure that the seat can operate well across a wide range of pressures. Very often, the low-pressure test is a more difficult test to pass due to the smaller closing force generated by the lower inlet pressure, as opposed to a high-pressure test, where the larger closing force may deform the seat around seat damage or debris, creating a seal even when the seat may be compromised.

pressure regulators

Figure 1. The components of a pressure-reducing regulator include: the set-pressure spring, which is the controlling mechanism; diaphragm, which is the sensing mechanism; seat; poppet, which is the sealing mechanism; body; body plug; inlet and outlet ports; threaded vent; and more
Swagelok

For either the low- or high-pressure test, the technician should first ensure sufficient supply pressure is available to the regulator to perform the tests and then screw the handle fully counterclockwise, allowing the poppet to fully close against the seat. For the low-pressure seat leak test, the technician should slowly raise the inlet pressure to approximately 14.5 psig (1 bar) on the regulator and allow the pressure to stabilize before checking for leaks. Once the inlet pressure is stabilized, the technician will monitor the regulator’s outlet pressure, watching for any increase that would indicate a seat leak.

For the high-pressure seat leak test, this procedure is repeated using the highest inlet pressure applicable for the regulator and system. After monitoring the regulator’s outlet pressure during this high-pressure test, the technician will know if the seat is installed properly, creating a seal even at the highest application pressure.

Shell leak test. To conduct a shell leak test, a technician will increase the regulator’s inlet pressure to approximately 29 psig (2 bars) and then close the downstream shutoff valve. Next, the technician will adjust the regulator handle to increase the outlet pressure to approximately 14.5 psig (1 bar) to ensure the regulator’s internal components are energized. Using a liquid leak detector, the technician will check for bubbles at the interface of the spring housing and body, the interface of the body plug and body (if equipped), and the spring housing weep hole (if equipped). Finally, the technician will repeat these procedures using the highest inlet and outlet pressures applicable for the regulator and system.

Other tests. While these two primary tests will help identify regulator leaks, maintenance technicians may need to dig deeper to diagnose other regulator anomalies. The following tests are not common, but may be necessary at times.

Overshoot test. If the regulator is slow to respond to pressure changes, a technician may perform an overshoot test. This test helps diagnose conditions such as a damaged O-ring that impedes the poppet’s natural action, a frozen regulator, or a weak poppet spring, all of which can affect the regulator’s ability to maintain a consistent setpoint pressure and potentially cause operators to make incorrect adjustments. To perform this test, the technician will set the regulator to a desired setpoint, shut off the upstream flow, and then vent everything downstream, so no pressure remains inside the regulator. Because the regulator is set, its poppet will remain open. The technician will then open the upstream isolation valve to reinitiate flow. With the poppet already open, the regulator poppet will need to adjust its position to regulate pressure at the new flow. Due to the short time the poppet needs to adjust its position, a downstream pressure spike above the regulator’s set point is possible. This spike is the overshoot value, which should ideally be no more than 5–10% above the regulator’s setpoint.

Lock-up test. If a large, abrupt change in pressure is observed when starting or stopping flow through a regulator, there may be a need to perform a lock-up test to help determine how much pressure the system loses when starting flow and how much the pressure increases when stopping flow. Some lock-up is acceptable, but it should be no more than 10% of the regulator’s control range, as high lock-up values can impede a regulator’s ability to maintain consistent outlet pressure. Lock-up, sometimes referred to as seat load drop, occurs when operating a regulator near its startup or shutoff point. When starting flow upstream, the downstream pressure will drop drastically until the regulator catches up to the newly applied force (see the seat load drop/lock-up zone noted at the far left of the regulator curve in Figure 2). The opposite scenario occurs when stopping downstream flow, as the regulator may suddenly snap shut as it approaches a no-flow state. In either case, the regulator may chatter or pulsate as it fluctuates between flow and no-flow conditions.

Figure 2.  This typical flow curve for a pressure-reducing regulator demonstrates how seat load drop, or lock-up, affects the regulator’s ability to maintain control near its startup and shutoff point. The diagram also shows the ideal operating area for the regulator, its flow coefficient (Cv), and the phenomena of outlet pressure droop and choked flow, which can both occur as flow increases

Figure 2. This typical flow curve for a pressure-reducing regulator demonstrates how seat load drop, or lock-up, affects the regulator’s ability to maintain control near its startup and shutoff point. The diagram also shows the ideal operating area for the regulator, its flow coefficient (Cv), and the phenomena of outlet pressure droop and choked flow, which can both occur as flow increases

If a regulator passes some or all these tests, the technician’s work may be completed until the next planned maintenance cycle. However, if leaks are uncovered during seat and shell testing, or the results of overshoot or lock-up tests are not satisfactory, the technician will need to investigate further.

 

Step 2: Inspecting regulators

Issues discovered during testing may warrant opening the regulator and examining its internal components for signs of debris, deformation, cracks, heavy chemical attack, or other damage. The three most common regulator components that require maintenance, in order of upkeep frequency, include the following:

Seat. The seat serves a sealing function that allows the regulator to contain pressure and prevents fluid from leaking to the opposite side of the regulator when flow is shut off. Common causes of leakage across the seat include debris stuck on the seat and damage. Either issue may prevent the regulator’s poppet from fully engaging in the seat and forming a complete seal. Sometimes a technician only needs to clear debris, clean the seat, and retest the regulator to fix the issue. However, damaged seats may require replacing.

Diaphragm. The diaphragm is the regulator’s sensing element and operates by flexing up and down to allow the regulator’s poppet to rise and fall within the seat to control outlet pressure. Debris may impact the diaphragm and, if found in the sensing chamber, should be cleared. However, it typically won’t affect the regulator’s sealing capabilities. More likely, a technician may find damage to the diaphragm from chemical seal degradation due to incompatibility with system fluids and/or evidence of stress from fatigue or overpressure (particularly when using a metal diaphragm regulator). These conditions will affect the diaphragm’s ability to adequately sense and respond to pressure fluctuations and may warrant replacing the diaphragm.

Poppet. In combination with the seat, the poppet both controls the outlet pressure while a system is flowing and completes the sealing process to prevent pressure from escaping to the regulator’s outlet port when flow is shut off. In a pressure-reducing regulator, the poppet is typically spring-loaded and held vertically in the inlet channel, with the tip in constant contact with the diaphragm. When closed, the poppet fits against a precision-machined seat and should create a high-tolerance seal. Any damage to the poppet, such as a deep scratch, may compromise that seal and necessitate a replacement. A poppet may also become stuck or hindered within its typical range of motion, in which case it should also be replaced, potentially along with the poppet spring and any associated O-rings.

 

Step 3: Maintaining regulators

Following inspection, a technician will need to determine whether it’s possible to replace a few select components to restore regulator functionality, or if it’s necessary to perform a major overhaul or even replace the regulator.

Per the CGA’s guidelines about regulators not having infinite service life, facilities should plan to maintain regulators periodically. Therefore, technicians should expect to replace components such as a regulator’s seat, diaphragm, poppet, springs or other components, depending on the demands of the application.

The CGA also notes that “materials used in regulators, particularly elastomeric or rubber materials, will deteriorate over time,” showing signs of “hardening, stress cracking and other physical property degradation.” For this reason, the association recommends replacing not just damaged components, but also any seals, backup O-rings, or other parts directly associated with the operation of that component. For example, when replacing a regulator’s seat, a technician should also replace the seat retainer O-ring, since the two components have a tolerance fit. Even if the O-ring appears to be in very good shape, it may have hidden wear and could be responsible for future seat leakage. Plus, since the technician already has the regulator open, it is likely less expensive to replace the O-ring at that time as opposed to waiting for a failure and incurring the additional expense of future maintenance downtime. Supporting the CGA’s recommendation, many manufacturers sell kits featuring the part being replaced as well as any associated components.

 

Step 4: Overhauling regulators

When replacing a few internal regulator components does not correct an issue, maintenance technicians may need to change all the regulator’s internal wear components. This overhaul could mean replacing the regulator’s range and poppet springs, spring plates, diaphragm, seat, poppet, seals and more — essentially anything that moves inside the regulator or is associated with a movement function. The few components that typically don’t need to be replaced include the regulator’s handle, body, spring cap and hardware.

Facilities should overhaul a regulator on a reactive basis when testing and inspection procedures indicate the need. The CGA also recommends overhauling a regulator at five-year intervals, but the time between service will vary based on application demands. To keep track of maintenance cycles, the CGA advises facilities to add tags to regulators that indicate their most recent maintenance service. Facilities should also add these data to their internal maintenance records to enable easier tracking and scheduling.

 

Step 5: Replacing regulators

Following testing and inspection, a technician may determine maintaining or overhauling a regulator is simply not feasible, in which case, the technician will install a new one. This practical decision may be based on the condition of the regulator, such as damaged threads that can’t be retapped or heavy chemical damage to components that can’t be replaced. It is also often driven by economics. Facilities will most commonly overhaul process-style regulators featuring ports that are 1-in. diameter or larger. Such regulators are typically expensive, so it is often more cost effective to replace all the internal components, compared to purchasing a new regulator. However, for smaller, instrumentation-sized regulators, it may be more feasible to simply replace the regulator and not spend the additional time replacing internal components.

 

Troubleshooting outcomes

When selecting a regulator for a fluid system, CPI plant operators must consider the total system design. That means addressing and understanding the function, material compatibility, ratings, installation, operation and maintenance of a regulator before making a choice. After the regulator is installed, their work is not complete. Maintenance personnel need to monitor the regulator and periodically test its performance to verify proper operation. These activities may reveal issues that require further inspection that may potentially result in some simple maintenance, minor component replacements, a complete overhaul, or even a full replacement. By following the five-step process noted above and learning the common symptoms and solutions associated with regulator performance, facilities can realize longer life cycles from these important components — and therefore reduce their overall operating costs. n

 

Author

Swagelok_JonKestnerJonathan (Jon) Kestner is product manager for regulators at Swagelok Company (29500 Solon Road, Solon, Ohio 44139; Phone: 440-248-4600; Email: jonathan.kestner@swagelok.com). He is responsible for assessing Swagelok’s regulator technologies, as well as creating development and commercialization plans for the product line. He also educates end users on best practices for regulator installation, operation, troubleshooting, and maintenance via training sessions and contributions to the Swagelok Reference Point blog (www.swagelok.com/blog). Kestner joined Swagelok in 2009 as a technical service representative and has also had roles as an inside technical sales engineer and field engineer. He holds a B.S.M.E. from Tufts University.

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