Round (circular) manways - Inoxmanways.com

What are round manways?

Round manways are the basic equipment of most stainless steel tanks. At the same time, this group of manways are the most numerous among all types of stainless steel manways. The number of designs, patterns, diameters and functionalities makes round manways the most versatile and universal group of products in the category of tank manways.

Round pressure manway

Round non-pressure manway

Among round manways, there are two basic groups:

non-pressure manways,
pressure manways.

In each of the groups mentioned there are manways equipped with hinged or non-hinged lids. The manway locking system, number of handwheels, handles, locking design and other manway components are selected depending on the diameter and application.

Selection parameters for round manways

In addition to the mentioned pressure parameter, other parameters such as:

dimension (diameter),
mounting method (top manway or side manway),
frame height and wall thickness,
construction material (AISI 304/304L or AISI 316/316L),
locking system (with handwheels, or clamp).

Below are selected parameters for the selection of round manways.

Dimensions of round stainless steel manways

Clearance diameter is one of the key elements in selecting a stainless steel manway. The offer includes both small size models (DN100-DN220) and popular diameters used in stainless steel tanks (DN300, DN400, DN420, DN450 or DN500).

Large diameter models for special applications and projects requiring an extra wide inspection opening round out the range. Among this type of models, there are all designs with diameters above DN600 (for example: DN800, DN1000, DN1200 or even DN1400).

Installation of round stainless steel manways

For round manways, the predominant installation method is mounting in the top (roof) of stainless steel tanks or process equipment. However, models designed for installation in the side (shell) of tanks are also available.

Round manways designed for top installation typically feature a lighter hinge design and, for non-pressure options, few handwheels or clamping points.

Round manway designed for top installation

Round manway for side installation

In contrast, the following features are often found with round manways for side installation:

number of clamping points around the perimeter of the manway is increased by using more handwheels or a lid cross bar,
the cover is completely removable or is fitted with a reinforced hinge,
the side manway group has a higher minimum pressure resistance threshold (due to naturally occurring fluid pressure inside the tank).

Frame height and wall thickness of round manway

Each round manway has a mounting element in the form of a frame. It is a part of a manway directly mounted in the surface of a tank or industrial equipment, in which an appropriately sized hole has been prepared in advance. Most often the mounting process is carried out by welding.

The range of the frame height parameter (often designated as "H") varies depending on the manway model. Most round manways include a height range of 60-150 mm in their specification. For standard models, the most common value is 60 mm. The designs of some manways provide for heights up to 250 mm, 500 mm or even 1000 mm. The frame height parameter is particularly important for thermally insulated tanks, where the thickness of the thermal insulation must be taken into account when fitting the equipment.

As important a parameter as the height of the frame is the thickness of its wall (often designated "SP"). The thickness of a manway frame can vary significantly depending on its intended use. For standard round stainless steel lids, this value will usually be around 2 mm. For pressure manways, the manway wall thickness is 8 mm, 10 mm or greater.

Locking systems for round manways

The vast majority of round manways have one of two types of locking systems:

with handwheels,
by means of a clamp.

Handwheels are the most common way to open and close a manway. This type of solution is used for both pressure and non-pressure manways. This is because it is common for the pressure resistance of a particular model to increase with the number of handwheels installed in it (more clamping points on the lid). So the non-pressure models will have one handwheel by default, while the pressure-resistant models will have: 4, 6, 8 or more handwheels arranged around the perimeter of the lid.

Round manway - locking by means of a clamp

Manway with handwheel locking

When choosing a manway with handwheel locking, be sure to choose the right handwheel material (typically: plastic or stainless steel). The main factors influencing the selection of an appropriate handwheel material are the temperature of the manway environment and the chemical reactivity of the medium with which the manway is intended to come into contact. The frequency of opening the lid is also important.

Another form of locking used on round manways is using a clamp. This solution involves connecting the manway frame and lid using a dedicated clamp that presses the two elements together around the perimeter of the manway. The main advantages of this solution are:

typically, the higher pressure resistance of lightweight round manways (as compared to handwheel versions),
speed of opening and closing the manway,
low minimum manway construction height (this is the main reason why manways with clamp locking are very often used in stackable pallet tanks),
possibility of achieving a hermetic seal and increased separation from external factors.

Round manway with clamp locking

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