If you work in pharmaceutical, biotech, food & beverage, or personal care manufacturing, you’ve almost certainly encountered diaphragm valves in your process piping systems. But what exactly makes them the valve of choice for high-purity applications? In this first post of our five-part series, we’ll break down the anatomy of a diaphragm valve and explain why it’s uniquely suited for sanitary process environments.

Three Components, One Valve

A diaphragm valve is fundamentally composed of three assemblies: the valve body (product contact), the diaphragm (product contact), and the topworks — sometimes called the bonnet or actuator (non-product contact). Understanding how these three elements work together is the key to specifying the right valve for your application.

The valve body provides the flow path and includes the weir — the raised ridge inside the valve that the diaphragm compresses against to shut off flow. The body also provides end connections (butt-weld, tri-clamp, or others) for tying into your process piping, as well as the bonnet flange that connects to the topworks above.

The diaphragm is the dynamic seal that enables and disables the flow path. It’s the only moving part in contact with the process fluid. When compressed against the weir, the valve is closed. When lifted, the valve is open. Diaphragms come in EPDM and PTFE varieties, each with different temperature ranges, chemical compatibility, and cycle life — we’ll cover these in detail in Part 4.

The topworks is the mechanism that moves the diaphragm. This can be a manual handwheel, a pneumatic actuator (fail-close, fail-open, or double-acting), or even an electric actuator. Switches and positioners can be added for feedback and control. We’ll dive into topworks in Part 5.

Why Choose a Diaphragm Valve?

Diaphragm valves dominate high-purity applications for three fundamental reasons:

Superior Drainability. The weir design, when the valve is properly installed, ensures maximum drainability — an essential factor in systems that must be fully evacuated between product changeovers or CIP (Clean-in-Place) cycles.

Application Versatility. Diaphragm valves handle a wide range of high-purity fluids: WFI (Water for Injection), purified water, buffer solutions, cell culture media, solvents, protein solutions, and more. They’re found in biotechnology, pharmaceutical, personal care, food & beverage, and brewery applications.

ITT Pure-Flo: Where They’re Made

ITT manufactures diaphragm valves at ISO 9001-2000 registered facilities worldwide. The Lancaster, PA facility is the Center of Excellence for both the EnviZion series and Pure-Flo series diaphragm valves, along with actuators and switches. Additional manufacturing is based in Obernkirchen, Germany, with ball valve production at Habonim, Israel, and a sales and manufacturing partnership with Tecnik Fluid Controls in India.

In the next post, we’ll take a deep dive into valve body specifications — materials, end connections, surface finishes, and configurations.

The valve body is where engineering meets regulatory compliance. Every spec decision — from material grade to surface finish to end connection type — directly affects your system’s cleanability, corrosion resistance, documentation burden, and overall cost. In this post, we’ll walk through the four key specification areas for ITT Pure-Flo valve bodies.

End Connections

ITT Pure-Flo valves are available in fractional sizes (0.25″, 0.38″, 0.5″, 0.75″) and standard sizes (1″, 1.5″, 2″, 2.5″, 3″, 4″, and 6″). End connection types include butt-weld/auto-weld, tri-clamp, and others such as SMS and flange connections. Butt-weld is the most common in pharmaceutical piping because it eliminates external crevices, while tri-clamp connections offer serviceability where frequent disassembly is required.

Material

316L stainless steel is the industry standard for BioPharm applications. High-grade alloys such as C22, C276, and AL6XN are available for aggressive chemical environments. What matters equally is the method of construction:

Forged Bodies (-F)

Forged bodies are the standard for 2-way valves in sizes 0.5″ through 4″. Forging provides critical advantages for sanitary applications:

ITT’s forging process has evolved from multi-piece welded construction to one-piece dedicated forgings. This evolution means a single CMTR (Certified Material Test Report) per body, shorter overall valve length, and compliance with ASME BPE fittings specifications for tangent length — all of which simplify documentation and reduce the total installed cost.

Wrought Bodies (-W)

Wrought construction (ASTM A479 316L) is used for block body valve configurations and 6″+ 2-way valves. Like forged bodies, wrought bodies have no porosity issues and can be mechanically or electropolished on both interior and exterior surfaces. Ferrite content is approximately 3%.

Surface Finish

Surface finish is measured as Ra (Roughness Average) in micrometres (µm) or microinches (µin). The Ra value is an average calculated from the peaks and valleys measured along a surface — the smoother the finish, the lower the Ra number.

Two polishing methods are used:

Why Circular Beats Linear on the Bonnet Flange

One detail often overlooked: the bonnet flange surface lay direction. A linear polishing pattern creates a potential leak path along the polishing lines — fluid can wick along the grooves. ITT addresses this with circular bonnet flange surfacing, which creates a concentric pattern that acts as a barrier to radial leak paths, providing a more reliable diaphragm seal.

Configuration

Beyond standard 2-way valves, ITT offers multi-valve fabrications and block body designs. These configurations are critical for minimizing dead legs in your piping system — a topic important enough to deserve its own post. That’s coming up next in Part 3.

Dead legs are the silent enemy of sanitary process systems. Per ASME BPE-2022, a dead leg is “a space where system design and operating conditions result in insufficient process fluid flow, presenting a risk for particulate, chemical, or biological contamination.” When you install multiple valves side by side — which happens constantly in pharmaceutical and biotech manifold assemblies — dead legs become a major design consideration.

The FDA Guideline: L ≤ 6D

The FDA’s 1993 guideline established the first widely adopted dead leg standard: the length (L) of unused pipe should be no more than 6 times the diameter (D) of that pipe. For years, this was the benchmark. But the bioprocessing industry found that the 6D standard wasn’t sufficient for optimal cleanable and sterilizable systems.

The BPE Guideline: L/D = 2:1

ASME BPE tightened the standard to an L/D ratio of 2:1 — meaning the dead leg length should be no more than twice the pipe diameter. ASME BPE-2019 Section SD-3.11.1 is clear: the system designer and manufacturer shall make every attempt to eliminate system dead legs, and must identify where exceptions exist or where the 2:1 target cannot be met.

Multi-Valve Fabrications

A multi-valve fabrication reduces dead legs by welding the second valve directly onto the D section of the first valve, eliminating the intermediate pipe run.

This gets you significantly better L/D performance than installing discrete valves side by side with pipe spools between them.

Block Bodies: Under 1D

Block body designs take dead leg reduction to the extreme. In an integrated block valve, the weir of the second valve is built directly into the weir of the first valve, achieving dead leg ratios of under 1D — effectively eliminating the dead leg entirely.

Here’s how the three approaches compare across common valve size combinations:

Valve Arrangement	½” × ½”	1½” × ½”	1″ × 1″	2″ × ½”
Sterile Access (SA) Array	5.5	5.5	3.0	6.0
GMP Array	3.9	4.0	2.8	4.0
Integral Sterile Access Block (ISG)	Under 1D	Under 1D	Under 1D	Under 1D

The data speaks for itself. Even the GMP array — which uses closer valve spacing than a standard Sterile Access array — often can’t meet the BPE 2:1 target. The ISG block body achieves under 1D across the board.

Custom Block Designs

ITT pioneered integrated valve technology and offers custom block body designs tailored to specific customer applications or P&ID layouts. If your process requires multiple sample points, purge valves, or branched manifold configurations, a custom block design may be the most effective path to BPE compliance.

In the next post, we’ll shift from bodies to the dynamic seal at the heart of every diaphragm valve: the diaphragm itself.

The diaphragm is the working heart of a diaphragm valve — the only moving component in contact with your process fluid. Selecting the right diaphragm material isn’t just a parts decision; it directly affects your maintenance intervals, chemical compatibility, temperature capability, and failure mode behavior. ITT Pure-Flo offers two primary diaphragm families: EPDM elastomers and PTFE composites.

Diaphragm Specification Fundamentals

Regardless of material, every diaphragm must meet three requirements: chemical resistance to the process fluid, the ability to withstand SIP (Steam-in-Place) temperatures — typically 250°F — and compliance with FDA 21 CFR Part 177 and USP 28 Class VI (Chapters 87 and 88) certifications.

E1 EPDM — The Next-Generation Elastomer

Specification	E1 EPDM
Sizes	1/4″ to 4″ Pure-Flo
Liquid Temp Range	-4°F to 194°F (-20°C to 90°C)
Continuous Steam	-22°F to 285°F (-30°C to 140°C)
Intermittent Steam	-22°F to 302°F (-30°C to 150°C)
Approvals	FDA, USP Class VI, EMEA/410/01 TSE/BSE Compliant
Shelf Life	6 years
Cure Method	Peroxide cured

The E1 uses a high molecular weight EPDM elastomer — longer molecular chains mean greater strength, toughness, and chemical stress crack resistance. The material can be stretched further before rupturing and withstands greater impact stress. It’s also peroxide cured, animal-derived-ingredient free, and EMEA/410/01 TSE/BSE compliant. ITT reports 2–5× cycle life in hot water applications compared to the previous Gr17 generation, with comparable steam capability.

TME PTFE — The Long-Life Champion

Specification	TME PTFE
Sizes	TME: 1/4″ to 4″ Pure-Flo; TMZ: 1/2″ to 2″ EnviZion
Temp Range	-4°F to 329°F (-20°C to 165°C)
Approvals	FDA, USP Class VI
Shelf Life	10 years
Backing	Gr B1 EPDM backing cushion

PTFE is chemically inert — there are essentially no chemical compatibility issues. It provides the longest life cycle of any available diaphragm material and features an advantageous failure mode compared to EPDM: when a PTFE diaphragm begins to fail, it tends to develop a slow weep rather than a sudden blowout, giving operators advance warning to schedule replacement.

Head-to-Head Comparison

Identifying Your Diaphragms

Knowing what’s installed in your valves matters during maintenance. EPDM diaphragms are identified by markings on the front and back — look for the E1 designation and a date code. PTFE diaphragms use a 2-character or 4-character date code system: the first character represents the month (A=January through L=December), followed by the year digit(s), and optionally a batch number. For example, B171 means February 2017, Batch 1.

In our final post, we’ll cover everything above the diaphragm: topworks, actuator types, switches, positioners, and how to size your actuators correctly.

The topworks is the brain and muscle of a diaphragm valve. Whether you’re operating manually with a handwheel or running fully automated with pneumatic actuators, electronic switches, and positioners, the topworks assembly determines how reliably, how precisely, and how safely your valve responds to your process control system.

In this final post, we’ll cover manual and automated topworks, key accessories, actuator sizing, and the critical terminology you need to know.

Manual Topworks

Manual topworks come in two flavors: rising stem and rising handwheel. Both use a compressor that pushes down on the diaphragm when the handwheel is turned clockwise, closing the valve. A visual indicator (the stem position) tells operators at a glance whether the valve is open, closed, or somewhere in between.

Automated Topworks

Automated actuators use pneumatic pressure to open or close the valve, with spring return to provide a defined failure position. There are three types:

Fail Closed (FC) / Air-to-Open (ATO)

Pneumatic pressure on the bottom compartment opens the valve against spring force. If air supply is lost, the spring closes the valve automatically. This is the most common configuration in pharmaceutical and biotech applications, where a loss of utilities should result in all valves defaulting to closed to protect the process.

The spring weight (60# or 90#) affects both the maximum operating line pressure and the amount of air required to open the valve.

Fail Open (FO) / Air-to-Close (ATC)

The reverse: pneumatic pressure on the top compartment closes the valve, and the spring holds it open on air loss. Used in applications where continuous flow must be maintained during utility failures — such as cooling water systems where shutting off flow could cause thermal damage.

Double Acting (DA)

Pneumatic pressure on both compartments — no spring. Often used in applications where the valve needs to hold its last position on air loss. External controls on the pneumatic lines can be configured to achieve fail-close or fail-open behavior as needed.

Key Accessories

Adjustable Travel Stop (ATS)

The ATS prevents over-closure of the valve by limiting how far the compressor can push down on the diaphragm. Without a properly set travel stop, excessive air pressure can compress the diaphragm beyond its designed stroke, shortening diaphragm life.

Setting the ATS on a 963 manual topworks involves loosening the lock nut, tightening the handwheel until the diaphragm seat is felt plus 5/8 turn, and then re-tightening the lock nut.

Adjustable Open Stop (AOS)

The AOS limits the opening stroke, restricting the fully-open flow rate. It’s used for flow balancing and throttling in manifold systems. Important: only adjust the AOS when the valve is at or near closed position. Rotate the indicating spindle counter-clockwise to restrict flow (spindle rises) and clockwise to increase flow (spindle lowers). Never force the AOS rotation.

Switches vs. Positioners

When specifying switches or positioners, consider: input voltage (DC vs. AC), output type (discrete ON/OFF or linear 4–20mA), digital protocol requirements (AS-i, DeviceNet, IO-Link, Ethernet), water ingression rating, and explosion-proof rating for hazardous environments.

Actuator Sizing

Correct actuator sizing ensures the valve can operate reliably at your process pressures. Actuator selection depends on five factors: valve size, diaphragm type (PTFE or EPDM), line pressure (Delta P), actuator type (FC, FO, or DA), and spring size (60# or 90#).

Understanding pressure drop is critical to actuator sizing. When there is equal pressure on both sides of the valve (P1 = P2), there is no pressure drop — and the actuator needs to overcome only the diaphragm and spring forces. When there is no opposing pressure on P2 (100% pressure drop), the full line pressure is working against the valve, and the actuator must overcome both the process pressure and the mechanical forces. Sizing charts are located in the Topworks section of the ITT Pure-Flo catalog and should be referenced for every application.

Valve Identification and Tracking

Every ITT Pure-Flo valve body is etched with its serial number, size, material, surface finish, cold working pressure, heat code, and optionally a customer tag number.

Receiving tags provide the complete figure number breakdown — body material, connections, surface finish, diaphragm type, actuator type, and more. Certificates of Compliance support multiple steps in the validation lifecycle (IQ, FAT, FRS, DDS, URS) and are available online along with material certificates at engvalves.com.

That wraps our five-part series on diaphragm valve basics. Whether you’re specifying new valves for a greenfield biotech facility or troubleshooting dead leg issues in an existing pharmaceutical plant, we hope this series has given you a solid foundation. If you have questions about ITT Pure-Flo diaphragm valves or need help with valve selection and sizing, our team is here to help.