Check Valve

Check valve is a kind of valve whose opening and closing parts are circular discs and act on their own weight and medium pressure to block medium backflow. It belongs to automatic valves, also known as check valves, one-way valves, return valves or isolation valves. Disc movement mode is divided into lifting type and swing type. Lift check valves are similar to globe valves in structure and lack only the stem that drives the disc. The medium flows in from the inlet (lower side) and out from the outlet (upper side). When the inlet pressure is greater than the weight of the disc and its flow resistance, the valve is opened. On the contrary, the valve closes when the medium flows back. Swing check valves have an oblique disc that can rotate around an axis and work in a similar way to lift check valves. Check valves are often used as bottom valves of pumping devices to prevent backflow of water. The combination of check valve and globe valve can play the role of safety isolation. The disadvantage is high resistance and poor sealing when closed.

Check Valve Parts

It is consist of body, cover, disk, hinge pin and seat ring. In the image belwo you can see the parts of the valve.

Image- TROUVAY & CAUVIN

Types of the Check Valve

Type of disk will decide the type of the valve. Most common types of Check valves are

• Swing Type.
  • Top Hinged
  • Tilting disk
• Lift Type
  • Piston Type
  • Ball type
• Dual Plate Type
• Stop Check Valve

Swing Check Valve

Image – DOE Handbook

The disc in a swing type valve is unguided as it fully opens or closes. This Valve operates when there is flow in the line and get fully closed when there is no flow. Turbulence and pressure drop in the valve is very low. Disk and seat designs can be of metal to metal or metal to composite.

The angle between the seat and the vertical plane is known as seating angle and vary from 0 to 45 degrees.  Usually, the seat angles are in the range of 5 to 7 degrees. Larger seat angles reduce the disc travel, resulting in quick closing, thus minimizing the possibility of water hammer. A vertical seat has a 0-degree angle.

Swing check valve allows full, unobstructed flow and automatically closes as pressure decreases. Usually installed in combination with gate valves because they provide relatively free flow combination.

A basic swing check valve consists of a valve body, a bonnet, and a disk that is connected to a hinge.

Materials

DN		15 – 600 mm
Pressure (MPa)		1.6	2.5	4.0
Test Pressure (MPa)	Body	2.4	3.75	6.0
	Seal	1.76	2.75	4.4
Temperature		-20°C – 200°C
Fluid		Oxygen
Body		Silicon Brass ZCuZn16Si4
Plug		Brass / Stainless Steel
Packing		Teflon (PTFE) / Nylon

Dimensions and Weights

Nominal Diameter ( mm )	Dimensions ( mm )									weight / Kg
	L	D	D1	D2	D6	b	Z-фd	D3	H
50	230	160	125	100	88	20	4-ф18	185	172	20
65	290	180	145	120	110	22	8-ф18	210	182	30
80	310	195	160	135	121	22	8-ф18	210	192	35
100	350	230	190	160	150	24	8-ф23	260	217	50
125	400	270	220	188	176	28	8-ф25	295	250	75
150	480	300	250	218	204	30	8-ф25	330	270	105
200	550	375	320	282	260	38	12-ф30	390	320	160
250	650	445	385	345	313	42	12-ф34	445	356	240

Tilting Disc Check Valve

Image – DOE Handbook

The tilting disc check valve is designed to overcome some of the weaknesses of conventional swing check valves. The design of tilting disk enables the valve to open fully and remain steady at lower flow rates and close quickly when the forwarding flow stop. The dome-shaped disc floats in the flow and fluid flow on both bottom and top of disk surfaces. As the disk is spring loaded, when forward flow pressure reduces, the spring force helps valve to close fast.  In the image above, you can see the flow from the valve.

Tilting Disc Check Valve are available in wafer type and lug type design.

Specifications

Part	Body	Disc	Seal-Ring	Stem	Packing
Material	Casting Iron	Casting Iron, Cast steel,Ductile	Oil-Resisting Chemigum, Chloroprene Rubber	Stainless Steel	PTFE

Materials

Model	PN(MPa)	Test pressure (MPa)		Working pressure	Medium temperature	Suitable medium
		Casing	Seal
H47X,H47H,HH47X, HH47XF ,HH47H, HDH47X	1.0	1.5	1.1	1.0	≤ 80 °C	Water, oil good, sea water, sludge
	1.6	2.4	1.75	1.6
	2.5	3.75	2.75	2.5

Dimensions

Ball Type and Plug Type Lift Check Valve

The seat design of a lift Check valve is similar to a Globe valve. A piston or a ball is usually used as a disk.

Lift Check valves are particularly suitable for high-pressure service where the velocity of flow is high. The disk is perfectly set on the seat with full contact. They are suitable for installation in horizontal or vertical pipelines with upward flow.

When the flow enters below the seat, a disk is raised from the seat by the pressure of the upward flow. When the flow stops or reverses, the backflow and gravity forced the disk downward to set on the seat. Commonly used in piping systems that used globe valves as a flow control valve.

Here you can see the plug or piston type and ball type check valve. These valves provide superior leak tight characteristics to those of swing check valves. Some design in plug type uses spring to retain the disk in closed position. This will ensure that valve allows flow only when there is enough pressure in the flow direction.

Ball type valve is very simple as it simply works on the principal of gravity. When there is enough pressure in the flow, it lifts the ball upward but when pressure reduced ball roll down and closed the opening.

Specifications

Model	PN(MPa)	Casting Test Pressure (MPa)	Seal Test Pressure (MPa)	Materials of Body, Bonnet
HQ41X-10	1.0	1.5	1.1	GG 25 / GGG 40
HQ41X-16	1.6	2.4	1.76

Dimensions

 

DN (mm)	L	D	D1	D2	Z-Φd	H
50	180	160	125	100	4-18	185
65	200	180	145	120	4-18	210
80	260	195	160	135	4-18/8-18	245
100	300	215	180	155	8-18	280
125	350	245	210	185	8-18	335
150	400	280	240	210	8-23	400
200	500	335	295	265	8-23/12-23	495
250	600	390/405	350/355	320	12-23/12-25	600
300	700	440/460	400/410	375	12-23/12-25	715
350	800	500/520	460/470	435	16-23/16-25	820

Dual Plate / Dual Disc Check Valve

A dual plate check valve is known as butterfly check valve, Folding Disc Check Valves, double-disc or split disc check valve. As the name suggests, two halves of the disk move towards centreline with the forward flow and with reverse flow two halves open and rest on the seat to close the flow (Flapping action).

Use of Dual Plate Check Valve is popular in low-pressure liquid and gaseous services. Its lightweight and compact construction make it a preferable choice when space and convenience are important. It is 80 to 90% lighter than conventional full body check valve. Frequently used in systems that used butterfly valves. The cost of installation & maintenance is very low compared to other types.

Stop Check Valve

Image- DOE Handbook

Stop Check Valve is a Combination of a lift check valve and a globe valve. It can either be used as a check valve or as an isolation (stop) valve like a globe valve. These valves can be closed with the help of a stem which is not connected to the valve disc during normal operation and make it possible to use these valves as a regular check valve. However, when needed, the stem is used to holds the free-floating disc against the valve seat, just as a globe valve. These valves are available in tee, wye, and angle pattern. Swing type and piston lift type check valves are commonly used as stop check valves.

Application of Check Valve (NRV)

Check valves (Non-return valve) are used in a piping system to prevent backflow. Discharge line of rotary equipment such as pump and compressor always fitted with a check valve to prevent backflow.

Advantages & Disadvantages

Can you guess why I have not mentioned any advantage or disadvantage of check valve?

The only function of a Non-return valve is to prevent backflow. There is no better alternative. Yes, you can choose the best check valve from the various available type that you have learned but you cannot supplement check valve with another valve.