PQ41F Blowdown Ball Valve

The PQ41F-16Q drain ball valve is a flanged, quarter-turn blowdown and drainage valve built for the lowest points of a pipeline or vessel, where water, steam condensate, oil or process fluid has to be evacuated quickly and completely. The one-piece body with a straight-through full bore drains without trapping fluid, and the QT450-10 ductile iron body with a 2Cr13 stainless ball and PTFE seats is rated PN16 to 200°C. Supplied in DN40 and DN50 — the two sizes most often drilled onto drain nozzles.

• Straight-through full bore — drains completely, no cavity to hold debris or standing fluid
• One-piece flanged body removes a potential leak path and stays compact in tight drain pits
• PTFE soft seats against a 2Cr13 polished ball give bubble-tight shut-off with low operating torque
• QT450-10 ductile iron body and bonnet, shot-blasted and coated for drain-pit and outdoor duty
• May be fitted in any orientation; the flow arrow should point toward the drain outlet
• PN16 (1.6 MPa), DN40–DN50, shell tested 2.4 MPa and seat tested 1.8 MPa per GB/T 13927

Product Overview

The PQ41F-16Q is a specialised drain and blowdown ball valve for water, steam, oil and non-corrosive fluid lines up to 200°C. Its compact one-piece body with a straight-through bore lets a pipeline section or vessel empty rapidly when a system is opened for maintenance or purged before commissioning. The body and bonnet are QT450-10 ductile iron; the ball and stem are 2Cr13 martensitic stainless steel; the seats and packing are PTFE. That combination gives dependable sealing at PN16 with a handle you can turn one-handed, which matters on a drain valve that is opened at the start of every outage.

Drain points are easy to specify badly: a valve that is too small leaves a puddle in the pipe, a throttled half-open ball erodes its own seat, and a drain left weeping between outages lets debris into the cavity. The PQ41F is sized for the common DN40 and DN50 drain nozzles, is meant to be run fully open or fully closed, and is shipped with the drain port guidance below so the installation behaves for years.

What the Model Code Means

The code follows GB/T 12237: Q = ball valve, 4 = flanged connection, 1 = straight-through bore, F = PTFE (fluoropolymer) seat; the leading P marks the drain / blowdown pattern, and 16Q = PN16 with a ductile iron body. See the Valve Model Decoder if you are matching another supplier’s coding.

Core Strengths

Dedicated Draining Function

Specially designed for pipeline draining and blowdown applications, the PQ41F-16Q features a compact one-piece body with a straight-through flow path that minimizes pressure drop and allows rapid, complete drainage of fluid from pipeline sections. The valve body geometry prevents fluid pockets and ensures full evacuation during maintenance or shutdown operations.

PTFE Soft Seating System

The precision-machined PTFE (polytetrafluoroethylene) seat ring provides bubble-tight shut-off against the 2Cr13 stainless steel ball. PTFE offers excellent chemical resistance, a low friction coefficient for smooth quarter-turn operation, and reliable sealing performance at temperatures up to 200°C and pressures up to 1.6 MPa.

Ductile Iron QT450-10 Body

The valve body and bonnet are cast from QT450-10 ductile iron, offering superior mechanical strength, impact resistance, and elongation compared to gray cast iron. This material is ideal for water, steam, and oil service up to 200°C, providing excellent durability and long service life in general industrial applications.

Stainless Steel Ball & Stem

The ball and stem are precision-machined from 2Cr13 martensitic stainless steel, providing excellent wear resistance, corrosion resistance, and hardness. The polished ball surface ensures consistent contact with the PTFE seat for reliable sealing across thousands of open-close cycles without galling or scoring.

Low Operating Torque

The combination of a precision-ground stainless steel ball and low-friction PTFE seating reduces operating torque significantly compared to metal-seated alternatives. The ergonomic lever handle provides positive quarter-turn operation with clear visual indication of valve position at both fully-open (handle parallel to pipe) and fully-closed (handle perpendicular).

Compact Flanged Design

The one-piece flanged body design eliminates potential leak paths from body-bonnet joints and provides a robust, compact form factor ideal for space-constrained installations. Standard GB/T 9113 flanged connections ensure compatibility with existing pipeline systems and easy installation without special adapters.

Performance Specifications

Parameter	PQ41F-16Q Specification
Nominal Pressure (PN)	16 (1.6 MPa)
Working Pressure	1.6 MPa
Shell Test Pressure	2.4 MPa
Seal Test Pressure	1.8 MPa
Working Temperature	≤200°C
Suitable Media	Water, Steam, Oil Products, Non-corrosive Fluids
Connection Type	Flanged (GB/T 9113)
Operation Mode	Manual Lever Handle (Quarter-Turn)
Seat Material	PTFE (Polytetrafluoroethylene)

PN16 only on this page. If your drain point sits on a higher-pressure line, tell us the design pressure: the PN25 and PN40 equivalents are built on the same pattern and are quoted as Q41F flanged ball valves with a drain arrangement.

Materials of Main Parts

Part Name	Material	Standard / Grade
Body & Bonnet	Ductile Cast Iron	QT450-10 (GB/T 1348)
Ball	Martensitic Stainless Steel	2Cr13
Stem	Martensitic Stainless Steel	2Cr13
Seat Ring	PTFE	Polytetrafluoroethylene
Packing	PTFE	Polytetrafluoroethylene
Handle	Steel with Plastic Coating	Q235 + PVC Coating

Main Dimensions & Connection Sizes

DN	L (mm)	D (mm)	D1 (mm)	D2 (mm)	b (mm)	f (mm)	n-φL
40	230	145	110	85	18	3	4×φ18
50	250	160	125	100	20	3	4×φ18

L = face-to-face length, D = flange outer diameter, D1 = bolt circle, D2 = raised face, b = flange thickness, f = raised face height, n-φL = bolt holes. Dimensions follow the GB/T 9113 PN16 flange pattern; certified drawings with flange drilling are issued with the quotation.

Drain Point and Blowdown Duty: Is This the Right Valve?

Two questions decide the selection, and getting them wrong is the most common cause of a leaking drain.

Duty	What to specify	Valve to quote
Routine drain of a water or oil line at ambient to 100°C	Full bore, PN16, ductile iron, lever handle	PQ41F-16Q in DN40 or DN50
Steam or hot condensate drain up to 200°C	Metal-backed seat materials and periodic purging to keep the bore clear	PQ41F-16Q, confirm the seat compound with us
Boiler blowdown at pressures and temperatures above 200°C	Purpose-made blowdown valves with extended bonnet and hardened trim	see the blowdown valve series
Drain on a line larger than DN50	Size to the nozzle, not to the valve already fitted	send the duty — we confirm availability or propose the Q41F equivalent
Drain that must modulate or be left part-open	Do not use a ball valve; throttling destroys the seat	a globe valve or control valve instead

Note the temperature limit honestly: saturated steam at 1.6 MPa is above 200°C, so the PQ41F is specified on drain and purge points inside its PTFE seat limit rather than on high-temperature boiler blowdown service, where our dedicated blowdown valves belong.

Structure Drawing

Design & Manufacturing Standards

• Design Standard: GB/T 12237 (ball valves)
• Face-to-Face Dimensions: GB/T 12221
• Flange Standards: GB/T 9113 (PN16)
• Testing & Inspection: GB/T 13927
• Ductile Iron Material: QT450-10 per GB/T 1348
• Applicable International Standards: API 6D, BS 5351 (optional)

Installation & Maintenance Guidelines

• Pipeline Preparation: Ensure pipeline ends are clean, free of welding slag, scale, and foreign debris before installation. Flush the pipeline thoroughly to remove any particles that could damage the PTFE seats during initial operation. Use proper gaskets matching the flange face type (RF).
• Installation Position: The PQ41F-16Q draining ball valve should be installed at the lowest point of the pipeline section or vessel to be drained. For horizontal pipelines, install with the valve body bore in the same horizontal plane as the pipe centerline. For vertical drain lines, ensure the valve discharges downward to allow gravity-assisted drainage.
• Flow Direction: Install the valve so that the flow arrow cast on the valve body points toward the drain outlet. While the ball valve is bidirectional, correct orientation ensures optimal drainage performance and prevents debris accumulation in the valve cavity.
• Flange Bolt Tightening: Align flange faces evenly before tightening bolts. Follow a cross-pattern tightening sequence in multiple passes to achieve uniform gasket compression. Do not fully tighten one side first as this causes body distortion and ball binding. Refer to bolt torque tables for the specific bolt grade and gasket material.
• Operating Instructions: Fully open or close the valve only — never use a ball valve for intermediate throttling as partially exposed seats will erode quickly from high-velocity flow. When opening for drainage, pause briefly at mid-position (45°) to equalize pressure across the ball before completing the turn. Always close slowly after drainage is complete.
• Packing Maintenance: Periodically check the stem packing area for signs of weeping or external leakage. If minor leakage occurs, gently retighten the packing gland nut by no more than 1/6 turn at a time while cycling the handle. Over-tightening will score the stem and increase operating torque. Replace packing rings if leakage persists.
• Seat Inspection: PTFE seats are subject to wear and cold-flow over extended service life, especially in high-cycle draining applications. Inspect seats annually for deformation, scratches, or compression set. Replace seat rings if the valve fails to hold seal test pressure. Always replace both upstream and downstream seats together.
• Drain Port Protection: When the valve is in the closed position for extended periods, ensure the downstream drain port is protected from debris ingress. Install a protective cap or short spool piece when the drain connection is not in use to prevent foreign material from entering the valve cavity.

Application Fields

The PQ41F is fitted where a system has to be emptied: Boiler Blowdown Systems, Pipeline Drain Points, Tank Emptying Connections, Steam System Condensate Drainage, Water Supply Network Purge Points, Oil Transfer Station Drain Lines, HVAC System Drainage, Process System Blowdown, Fire Protection System Drainage, Industrial Pipeline Maintenance. It is a maintenance valve rather than a process valve, and it earns its keep by draining fast and then holding tight until the next outage.

What We Need to Quote Your PQ41F Drain Valves

• Size and quantity: DN40 or DN50, mixed quantities welcome.
• Line pressure and temperature: PN16 standard; confirm anything outside 1.6 MPa or 200°C.
• Medium: water, condensate, oil or process fluid, and whether it carries solids.
• Flange standard: GB/T 9113 as standard; EN 1092 or ASME B16.5 on request.
• Operation: lever as standard; extended handle or gearbox for buried or high drain points.
• Accessories: drain cap, spool piece, or a hose tail connection if the drain discharges to a collection line.
• Documentation: EN 10204 3.1 certificates and test records for tender packages.

Send the pipe and instrument drawing or just the nozzle size and duty, and we will confirm the valve, the seat compound and the face-to-face in one reply. Datasheets are in the download center and qualifications on the certifications page.

Frequently Asked Questions

What is the difference between a drain valve and a blowdown valve?

A drain valve empties a line or vessel by gravity or residual pressure, usually at moderate temperature. Blowdown discharges a boiler or vessel under pressure and high temperature, which erodes soft seats and needs a purpose-built valve with extended bonnet and hardened trim. The PQ41F covers drain and purge duty inside its 200 degC seat limit; above that, use our dedicated blowdown valve series.

Why only DN40 and DN50?

Those are the two drain nozzle sizes most pipe specs already carry, so the valve drops onto an existing nozzle without a reducer. For a larger drain point, tell us the line size and duty and we will confirm a larger drain pattern or quote the equivalent Q41F flanged ball valve.

Can the PQ41F be installed in any direction?

Yes, the body can be fitted in any orientation, which is useful in a drain pit. Set the cast flow arrow toward the drain outlet so the bore drains clear and debris is not held in the body when the valve closes.

Can I use it to control the flow rate while draining?

No. Run it fully open or fully closed. Held part-open, the medium washes across the exposed edge of the PTFE seat, which erodes it and leaves the valve leaking when closed. For throttling duty specify a globe valve.

How do I keep a drain valve from leaking between outages?

Close it fully, protect the drain port from debris ingress with a cap or short spool, and cycle it open and closed once a year so the stem packing is not left set in one position. If the gland weeps, tighten it in increments of no more than a 1/6 turn while cycling the handle.

Are the seats field replaceable?

Yes. The bonnet is bolted, so the valve stays in the line while the seats are changed. Replace upstream and downstream seats as a matched pair and rebuild with PTFE-compatible grease.

Get a Quote & Technical Support

Contact Gaoshan Valve for dimension sheets, CAD drawings, material certificates and a sized recommendation for your drain and blowdown points. Reply within 24 hours from our overseas sales desk.