The Spirax Sarco KBV21 is a manual boiler blowdown valve comprising a carbon steel ball valve with a reinforced PTFE seat and a stainless steel manual handle. Designed specifically for boiler blowdown applications, it is particularly suitable for systems that do not require timed automatic blowdown. A key safety feature of the KBV21 is its interlock mechanism: the manual handle cannot be removed when the valve is open, ensuring strict compliance with boiler house regulations.

Two types of handles are available (supplied separately): a standard length handle and an extended 'T' handle for blowdown valves located in restricted spaces.

Key Features

• Designed specifically for boiler blowdown applications.
• Suitable for boiler pressures up to 17.25 bar g at 208°C.
• Size range from DN25 to DN65.
• Safety interlock: The handle can only be removed when the valve is in the fully closed position.
• Clear markings indicate the OPEN and CLOSED positions of the valve.
• A 90° rotation from fully open to fully closed ensures correct "rapid blowdown" operation.

Sizes and Pipe Connections

• Sizes: DN25, DN32*, DN40, DN50, DN65
• Connections: Flanged BS4504 PN40 or BS1560 Class 300

Note: DN32 is available in PN40 only.

Limiting Conditions

Parameter	Value
Maximum Allowable Pressure	17.25 bar g at 208°C (250 psi g at 406°F)
Cold Hydraulic Test Pressure	60 bar g (PN40) 78 bar g (Class 300)
Seat Leakage Test	6 bar g (Air under water)

Materials

Part	Material	Standard
Body	Carbon Steel	ASTM A216 WCB
Seat and Stem Seal	Reinforced PTFE	-
Ball	Austenitic Stainless Steel	AISI 316
Stem	Stainless Steel	AISI 420 or 316
Sleeve	Austenitic Stainless Steel	AISI 316L
Connector	Austenitic Stainless Steel	AISI 316L
Standard Handle*	Austenitic Stainless Steel	AISI 316L
'T' Handle*	Carbon Steel	-

Note: Standard handle and 'T' handle are supplied separately.

Dimensions and Weights

Approximate dimensions in mm and weights in kg.

Size	A	B	C	D	E	F	Weight
DN25	165	114	35	-	-	21	6.0
DN32	178	117	35	-	-	23	7.5
DN40	190	126	35	-	-	31	9.8
DN50	216	134	35	-	-	38	12.0
DN65	241	146	35	-	-	51	18.0
Standard Handle*	-	-	-	32	258	-	-
'T' Handle*	-	-	-	500	375	-	-

Installation

WARNING

Ensure the boiler is drained and vented to atmosphere before installation or maintenance.

Check that the blowdown valve and inlet pipe sizes match. Determine the correct pipe length and align the pipe with the valve center to avoid stress. The valve must be installed in the direction of fluid flow as indicated by the arrow.

Handle Assembly Installation

1. Ensure the valve is in the closed position. (If the operating handle is installed, it should be at 90° to the valve centerline).
2. Remove the stem nut (7/8" A/F), spring washer, and operating handle (if fitted).
3. Remove the stop bolt (1/2" or 7/8" A/F) (if fitted).
4. Check the gland nut torque is 24-30 Nm (18-22 lbf ft).
5. Install the lock nut (7/8" A/F) to prevent the gland nut from loosening. (For DN25 and DN32, install the lock nut as above).
6. Place the connector into the sleeve and align the inner groove of the connector with the stem. Ensure the threaded holes of the body align with the cutouts on the sleeve.
7. Install the washers and cylindrical hex bolts (7/32" or 5/16" A/F). Tighten, then turn a further 1/4 turn.
8. Insert the operating handle (supplied separately) and check that the handle can only be removed when the valve is closed.

Maintenance

It is recommended to check the valve for debris and corrosion during boiler overhauls. Check the stem for leaks. If there is a minor leak, tighten the gland nut to a torque of 24-30 Nm (18-22 lbf ft).

DANGER

The ball valve may trap pressurized media within the valve cavity. Ensure there is no pressure at the valve inlet, outlet, or inside the valve before loosening and removing the flange bolts.

If the valve requires re-polishing (or just removal for inspection), a special tool is required to remove the screwed-in insert. This tool can be made from a steel plate of suitable thickness (with rounded corners) to fit into the corresponding holes of the seal packing.

For blowdown applications, carbon-reinforced PTFE stem seals should be used instead of graphite seals.

Dismantling the Body

Use the special tool to remove the insert contained in the valve. Significant force may be required to open the joint; use a vice if necessary. Penetrating oil can be used to help remove the seal packing, but do not use heat.

DANGER

If aged fluoroelastomer 'O' rings are exposed to temperatures of 315°C (599°F) or higher, they may decompose and produce hydrofluoric acid. Avoid skin contact and inhalation of any fumes, as this acid can cause severe burns and damage the respiratory system.

Once the insert is removed, the ball can be taken out. To remove the stem, first loosen the lock nut and gland nut, then gently tap the stem into the body using a soft-faced hammer to avoid damaging the stem threads.

Spare Parts

A complete set of spare parts is available, including all seal packings, gasket kits, and the valve ball. Stem spares are also available.

INFO

The vent hole on the ball must be on the upstream side of the valve.

When ordering, please specify the valve type, application (e.g., boiler blowdown), and size (DN).