--- title: "Pressure vs. Non-Pressure Manway Covers: What's the Difference?" date: 2026-07-01T03:24:48Z modified: 2026-07-16T03:29:45Z permalink: "https://www.hyflowtech.com/blog/basic/pressure-vs-non-pressure-manway-covers/" type: post status: publish excerpt: "" wpid: 1983 categories: - basic featured_image: "https://www.hyflowtech.com/wp-content/uploads/2026/07/image-94-e1784169869851.webp" featured_image_alt: three types of manway covers timestamp: 2026-07-16T03:29:45Z tags: - basic --- This guide compares pressure and non-pressure manway covers for industrial tanks, helping you determine whether your vessel needs a certified pressure vessel manway or a standard atmospheric hatch. Choosing the right type not only ensures operational safety. It also provides regulatory compliance. Pressurized systems require certified designs to prevent dangerous tank ruptures. Atmospheric systems offer lighter, economical access for standard storage tanks. ## Covers for Pressure Manway Vessels A pressure manway cover is a sealed closure engineered for pressurized process tanks. These units operate under internal forces that can reach full vacuum conditions. Industrial reactors, fermenters, and pharmaceutical tanks are the most common applications. Any tank that runs pneumatic filling, nitrogen blanketing, or steam CIP cycles will require this type of closure. Manufacturers build these covers from thick, high-strength alloy plates and use heavy-duty clamps like swing bolts, cam locks, or davit arms to compress the gasket under load. The specific differences in hardware, certification, and cost are covered in the comparison below. ## Covers for Non-Pressure Vessels A non-pressure manway cover is an access hatch for atmospheric storage systems. These covers operate near atmospheric pressure, usually between 0 and 1 psi. Clean water storage tanks, open reservoirs, and gravity-fed mixing tanks are the typical applications. These hatches prioritize quick, frequent access for cleaning and inspection over pressure containment. An atmospheric manhole tank cover uses thin steel sheets and simple latches to keep out debris and rainwater. Standard non-pressure round manway cover vessels provide economical options where internal force is not a concern. ## Key Differences Between Pressure vs. Non-Pressure Manway Covers Operating pressure is the starting point, but it is not the only factor that separates a [pressure manway cover](https://www.hyflowtech.com/product/sanitary-pressure-manway-cover/) from a standard atmospheric hatch. Once you compare the two side by side, the differences show up in structural design, sealing method, certification requirements, and how each type is specified on a purchase order. We break down each difference below based on what our engineering team sees most often in customer RFQs. ### Quick Comparison | **Parameter** | **Pressure Manway Cover** | **Non-Pressure Manway Cover** | | --- | --- | --- | | Typical Operating Range | Above 15 psi, or full vacuum | 0–1 psi (near atmospheric) | | Shape | Circular/domed | Flat or slightly crowned | | ASME Code | Section VIII Division 1 | Not applicable | | Common Seal Materials | EPDM, PTFE, Viton | EPDM, Silicone | | Typical Fasteners | Swing bolts, davit arms, cam locks | Simple latches or bolts | | Surface Finish (sanitary) | Ra ≤ 0.8 µm, electropolished | Mill finish / 2B acceptable | | Weld Inspection | Radiographic or dye-penetrant required | No mandatory post-weld inspection | | Integrated Safety Devices | Relief valve, rupture disc port, interlock | Breather vent or overflow spout | | Typical Use Case | Reactors, fermenters, pneumatic-filled tanks | Water storage, open reservoirs, gravity-fed tanks | | Relative Cost | Higher (certified design + hardware) | Lower (simpler fabrication) | ### Structural Design and Wall Thickness Pressure vessel manway covers are built to contain internal force in every direction. That is why they are almost always circular or domed rather than flat. The curved geometry distributes stress evenly across the plate. This lets engineers use thinner material than a flat design would require at the same strength rating. Non-pressure round manway cover vessels don’t carry this structural burden. Since they operate at or near atmospheric pressure, a flat or slightly crowned plate is sufficient. This keeps material and fabrication costs down. In practice, we see pressure manway vessels specified at 4–6 mm plate thickness for sanitary applications, while atmospheric covers of the same diameter often come in at 2–3 mm. ### Sealing and Closure Mechanism This is where the two diverge most visibly on the shop floor. A pressure vessel manway relies on compression-based sealing — swing bolts, davit arms, or cam locks that clamp the gasket under continuous load. The gasket must hold pressure or vacuum without creeping open during operation. An atmospheric manhole tank cover uses simple latches, wing nuts, or hinge clamps. Its gasket only needs to keep out dust, rain, and insects rather than resist internal force. One common mistake we see in RFQs: buyers spec a cam-lock closure on an atmospheric tank where a simple latch would do. This adds unnecessary cost without improving performance. ### Certification and Code Compliance Pressure manway vessels used in regulated industrial processes typically fall under ASME Section VIII Division 1. European buyers also need PED 2014/68/EU compliance. These codes require design calculations, material traceability, and often hydrostatic or radiographic testing before the tank can be stamped. Non-pressure covers carry no such code obligation. There is no ASME classification for atmospheric hatches, which is one reason they cost less and ship faster. ### Surface Finish and Sanitary Requirements Pressure vessel manway covers used in food, dairy, or pharma processing must meet strict surface finish specs — typically Ra ≤ 0.8 µm on all product-contact surfaces. Electropolished internals eliminate micro-pitting where bacteria can harbor. The cover’s inner radius, gasket groove, and hinge bracket all fall under this finish requirement. Non-pressure round manway cover vessels on water or utility tanks rarely carry a surface finish callout. Mill finish or standard 2B stainless is usually acceptable, which cuts polishing cost from the unit price. From our production experience, electropolishing adds roughly 15–20% to the unit cost. If your application doesn’t require it, specifying 2B finish saves budget without compromising function. ### Connection Method to the Tank How the cover attaches to the tank shell differs significantly between the two types. Pressure manway covers are welded onto a reinforced nozzle neck that has been pre-calculated for the tank’s MAWP. The weld joint itself often requires radiographic or dye-penetrant inspection before the tank passes code. An atmospheric manhole tank cover typically mounts on a simpler welded collar or flanged ring. No post-weld inspection is mandated, making installation faster and less expensive. ### Safety Features and Pressure Relief Pressure manway tanks on process vessels often integrate a [pressure relief valve](https://www.hyflowtech.com/product/sanitary-automatic-pressure-relief-valve/), rupture disc port, or vacuum breaker directly into the cover assembly. This gives the tank a controlled venting path before internal force reaches a dangerous level. Some designs also include a safety interlock that prevents the cover from being unlatched while the tank is still pressurized. This protects maintenance personnel during entry. Atmospheric covers don’t require these devices because the tank operates at ambient pressure. A simple [breather vent](https://www.hyflowtech.com/product/sanitary-tank-vent-breather-valve/) or overflow spout is common on water tanks to prevent minor vacuum during drainage. ### Opening Size and Orientation Both types come in standard diameters — 150 mm, 200 mm, 300 mm, 400 mm, 500 mm, and 600 mm are the most common in sanitary applications. However, pressure vessel manway covers are more commonly installed on the top head or side shell of vertical tanks. The cover must resist both internal pressure and its own dead weight when opened. Non-pressure covers appear more often on top-mounted positions on horizontal or open-top tanks. Gravity keeps the cover seated, and a single hinge allows one-handed operation for frequent access. When our customers request side-mounted manways above 400 mm, we typically recommend a davit arm to handle the cover weight safely — this is especially important on pressure manway vessels where the cover plate is heavier. ### Gasket Life and Replacement Cycle Gasket performance diverges sharply between the two applications. On a pressure vessel manway, the gasket compresses under heavy bolt load at every closing cycle. It must hold that seal against sustained pressure or vacuum between maintenance intervals. Typical replacement cycles run every 12 to 24 months, depending on chemical exposure and temperature swings. On an atmospheric manhole tank cover, the gasket load is minimal. But the gasket may see far more open-close cycles per week if operators access the tank daily for cleaning or inspection. In this case, mechanical wear rather than chemical degradation drives the replacement schedule. We advise buyers to keep one spare gasket set per manway on site. A failed gasket on a pressure manway vessel system means a full production shutdown until the seal is replaced. ### Weight, Cost, and Lifecycle Because of the thicker alloy plate and certified hardware, pressure covers run heavier and carry a higher unit cost. But they are a one-time capital cost tied to a tank’s design life. Non-pressure round manway cover vessels are lighter and cheaper individually. But on high-cycle applications like water tanks that get opened daily for inspection, latch wear and gasket replacement become a recurring maintenance line item. Over a 10-year vessel life, the total cost of ownership on a frequently opened atmospheric cover can approach that of a pressure-rated unit — factor in replacement parts when comparing quotes. ### Which One Does Your Application Need? If your vessel is pneumatically filled, holds volatile or fuming chemicals, or operates above 15 psi, a pressure vessel manway is the only design that will hold code and prevent rupture. If you’re storing water or low-hazard fluids in a gravity-fed or low-rate-pumped tank, an atmospheric manhole tank cover gets the job done at a fraction of the cost and lead time. When you’re not sure which category your system falls into, send HEYI your operating pressure range and fill method. Our engineering team will confirm the correct spec before you order. ## Common Mistakes in Manway Cover Selection Choosing the wrong manway cover is one of the most preventable — and most expensive — failures in tank specification. Here are the errors our engineering team sees most often in customer RFQs. ### Mistake 1: Installing an atmospheric cover on a pressurized system This is the most dangerous one. An atmospheric hatch cannot hold internal force. The result is structural collapse, physical deformation, and volatile leaks. We have seen this happen when a plant upgrades its filling method from gravity to pneumatic but doesn’t revisit the manway spec. Rapid pumping creates sudden vacuum conditions inside the tank. Without a pressure-rated closure and adequate venting, the tank implodes. ### Mistake 2: Selecting the wrong gasket material Corrosive chemicals degrade incompatible seals over weeks, not months. The joint starts weeping before anyone notices. Before purchasing any pressure vessel manway or atmospheric manhole tank cover, verify two things: the chemical compatibility chart for your gasket material, and the maximum operating temperature your seal will face. If your process runs both acid and caustic CIP cycles, [PTFE ](https://www.hyflowtech.com/product/ptfe-flange-gasket/)or Viton is usually the safer choice over standard EPDM. ### Mistake 3: Over-specifying the cover This one costs money instead of safety. Buyers sometimes request a full pressure manway vessel assembly for a simple water storage tank. The result is unnecessary cost, longer lead time, and heavier covers that operators struggle to open daily. Match the spec to the actual operating condition — not the worst-case scenario you’ll never run. ### Mistake 4: Ignoring access frequency when choosing fastener type A swing-bolt closure is robust, but if your operators open the manway twice a day for inspection, they will start skipping bolts to save time. That defeats the seal. For high-frequency access on non-pressure round manway cover vessels, specify a quick-release clamp or single-lever latch. For pressure manway vessels that still need regular entry, a davit arm with cam-lock reduces opening time while maintaining full seal compression. ## How to Choose the Right Manway Cover Selecting the correct cover comes down to three parameters: tank operating pressure, chemical hazard level, and how often the cover gets opened. ### Choose a pressure vessel manway when: Your system operates above 15 psi or under vacuum. Pneumatic filling, nitrogen blanketing, or steam CIP cycles are part of your process. The tank holds volatile, fuming, or rapidly decomposing chemicals that generate internal pressure. In any of these cases, a certified pressure manway is not optional. It is the only design that prevents rupture and meets ASME or PED code. ### Choose an atmospheric manhole tank cover when: Your tank operates below 1 psi with gravity feed or low-rate pumping. The stored fluid is water, mild chemical solution, or other low-hazard product. Operators need quick, frequent access for cleaning and inspection without unbolting heavy swing bolts every time. These non-pressure round manway cover vessels keep costs down and allow one-person operation on routine maintenance rounds. ### Still not sure? Send HEYI your process data sheet or tank drawing. Our engineering team will confirm which pressure class your manway needs, recommend the right gasket material for your chemical environment, and quote the correct unit — typically within 24 hours. ## Partner with HEYI for Certified Access Solutions [ ![Wholesale Stainless Steel Sanitary Manway Covers and Valves](https://hyflowtech.b-cdn.net/wp-content/uploads/2026/05/%E5%85%A8%E8%A7%86%E9%95%9C%E4%BA%BA%E5%AD%94sigh-glass-manhole-cover.png) **Sanitary Manway Covers** B2B catalog for global buyers, featuring various stainless steel sanitary manway covers and fluid valves for quick specification and inquiry. Explore Catalog ](https://www.hyflowtech.com/wp-content/uploads/wp-mfa-exports/taxonomy/product_cat/sanitary-manway-covers.md) Not sure whether your tank needs a pressure vessel manway or an atmospheric manhole tank cover? Send us your operating pressure, fill method, and chemical environment — our engineering team will confirm the correct pressure class and gasket material before you order. HEYI manufactures both pressure-rated and non-pressure manway covers in-house, with full GMP/FDA/3A certification. Standard sizes ship in 1–7 days. Custom specs deliver in 15–35 days. [Get a Quote](https://www.hyflowtech.com/wp-content/uploads/wp-mfa-exports/page/contact-us.md) | [View Full Product Catalog](https://www.hyflowtech.com/wp-content/uploads/2026/06/HEYI-MANHOLE-COVER-CATALOG.pdf) [ Contact US ](https://www.hyflowtech.com/wp-content/uploads/wp-mfa-exports/page/contact-us.md)