BACK

Q&A – EPR and Pressure Limiting Valves w/ Matthew Taylor

By Bryan Orr Matthew Taylor

Make & share a podcast clip

Keep the exact passage and a link to the full episode. Choose up to three minutes, with enough context to be fair to the speaker.

Start End

Preview uses this episode’s audio. Browser audio export, when supported, takes the length of the selected clip. Nothing plays until you choose Preview.

In this episode, Matthew Taylor joins the podcast to dive deep into the world of pressure-limiting valves and regulators used in refrigeration and air conditioning systems. They explore the intricacies of Maximum Operating Pressure (MOP) expansion valves, Evaporator Pressure Regulators (EPR), and Crankcase Pressure Regulators (CPR), discussing their functions, applications, and differences.

The conversation begins with an explanation of MOP expansion valves, which are commonly used in low-temperature refrigeration applications and air conditioning systems. Matthew describes how these valves work by using a vapor-charged thermal element to limit the suction pressure, protecting compressors from operating outside their designed range. They discuss the differences between liquid-filled, vapor-charged, and cross-charged valves, highlighting how each type affects system performance and superheat control.

The discussion then shifts to larger systems and rack refrigeration, where Crankcase Pressure Regulators (CPRs) are preferred over MOP valves. Matthew explains how CPRs control pressure closer to the compressor, allowing for better superheat control in systems with longer piping runs. The conversation concludes with an explanation of Evaporator Pressure Regulators (EPRs), which are used in multi-evaporator systems to maintain specific evaporator temperatures independently of the overall system suction pressure.

Topics covered in the podcast:

Maximum Operating Pressure (MOP) expansion valves
Liquid-filled vs. vapor-charged thermal elements
Cross-charged valves and superheat control
Applications of MOP valves in small refrigeration systems and air conditioning
Crankcase Pressure Regulators (CPRs) for larger systems
Evaporator Pressure Regulators (EPRs) for multi-evaporator setups
Differences between MOP, CPR, and EPR in pressure control
Challenges of pressure control in rack refrigeration systems
Impact of pressure-limiting devices on compressor longevity
Considerations for technicians when working with different types of systems

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Purchase your tickets or learn more about the 6th Annual HVACR Training Symposium at https://www.hvacrschool.com/symposium.

Subscribe to our podcast on your iPhone or Android.

Subscribe to our YouTube channel.

Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

Work through this with the trade.

Highlight a short passage, or bring a question about a specific moment into HVAC No Bull Forum.

Discuss this reference → Related forum discussions

Comments

Uncovering the Root Causes of Commercial Refrigeration Failures

Why and How to Test Heat Pump Defrost – Short #310

Building a Business That Lasts: Why Culture Beats Strategy in HVACR w/ Tony Gonzalez

Tight Enough to Fail – Short #309

Glycol Skids for Market Refrigeration w/ Max Johnson

Your Thermostat Is Reading the Wall – Short #308

Next-Gen Filtration – Pressure Drop, MERV 16, and Bypass Prevention w/ Chris Howells

The Fuse Only Blows When You Leave – Short #307

Questionable CO Alarms w/ Bill Spohn

Same Charge, Different Numbers – Short #306

#cpr #crankcase pressure regulators #EPR #evaporator pressure regulator #maximum operating pressure #mop #refrigeration

Author:

Bryan Orr

Company: Kalos Services

Position: Co-Founder and President

Matthew Taylor

Company: Kalos Services

Position: Commercial Refrigeration Service Manager

Check out our most recent video

How to Evacuate an AC system, Full Vacuum Procedure

Our latest Podcast

HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this live stream, co-branded with Kalos, Bryan Orr sits down with Kalos refrigeration team members Christian Maitland and Alex Orr to talk about the realities of working on market refrigeration systems. The conversation starts with the rapid arrival of new equipment in grocery stores, especially transcritical CO2 racks, and why even well-trained techs are running into problems nobody has seen before. Because these are engineered, built-up systems rather than mass-produced units, the first real stress test often happens in the field, during installation and startup.

The group digs into where those problems actually come from. Some are classic installation errors, like skipping nitrogen purges while brazing, leaving burrs in pipe, or forgetting that ACR copper plugs sit on the inside of the pipe. Others trace back to the manufacturer: sensors landed on the wrong terminals, swapped sensors that left a condenser fan unable to run, controllers that overheat and reset, and programming that was tested in a different climate than the one the equipment ends up in. With multiple manufacturers supplying the rack, controller, and condenser, nobody owns the interface between the pieces, so startup techs end up tuning parameters store by store.

Bryan, Christian, and Alex also walk through the root cause process they rely on, which is essentially the scientific method: observe the complaint, form a hypothesis, test it, and then keep digging until you know why it happened and can confirm the fix on the next job. They discuss store dew point and airflow as the most common causes of iced-up and sweating cases, a humbling misdiagnosis involving a transducer and a redundant controller, and the pain of 19-week lead times and wrong parts arriving seven times in a row.

The episode closes with practical advice for techs. Walk into every store and use your senses, check behind your install team, pull your vacuums, and document conversations with customers when expectations don’t match the equipment specs. Christian encourages techs to share what they learn with peers, Alex reminds listeners that solving ridiculous problems is the job and a chance to be the hero, and Chad’s late addition is a reminder that equipment should be designed for worst-case conditions rather than a design day.

Topics Covered

Transcritical CO2 coming to the U.S. market, and why it behaves differently above roughly 86°F
Challenges of high ambient temperature and humidity in Florida, including limits of adiabatic cooling
Controllers that overheat and reset, and how quickly a CO2 system can lose its charge when that happens
Safety and mindset for techs moving from traditional DX to high-pressure CO2 systems
Why built-up systems get their first real field test at installation and startup
Clean piping practices: nitrogen purging, burrs, carbon buildup, and tiny orifices in ejectors and microchannel coils
The pipe plug in the EPR story and other lessons from early grocery work
Manufacturer errors caught at startup, including miswired harnesses and swapped sensors
Interconnected controls from different manufacturers and the need for site-specific programming
Setting customer expectations on case placement, shelving, and spec limits, and documenting those conversations
Store dew point, dehumidifiers, and ceiling fans disrupting open-case air curtains
Using building science tools like smoke pens and vane anemometers on refrigeration cases
The root cause process: observe, hypothesize, test, find the real cause, and verify the fix
A transducer misdiagnosis and why to rule out everything before ordering long-lead-time parts
Parts lead times, wrong parts, and the hidden labor cost of learning new equipment alongside manufacturers
Commissioning during live-store case swaps, and the gap in manufacturer training for new equipment
What techs look for on a first walkthrough, plus startup checks like line sizing, case assembly, and pulling vacuums
Gaps in tools, such as digital gauges built for transcritical systems
Closing takeaways: share knowledge with peers, own the problem, and design equipment for worst-case conditions