Danfoss POV Data sheet
Data Sheet
Compressor overflow valve
Type POV
Designed for protecting compressors against excessive pressure
The POV compressor overflow valve is used in conjunction with the BSV safety relief valve and is specifically designed for protecting compressors against excessive pressure.
Features
• Applicable for the refrigerants HCFC, HFC, R717 (Ammonia), R744 (CO2).
• The Pilot Operated Internal compressor overflow valve System POV + BSV is available in sizes from DN 40 to DN 80.
• POV + BSV is an internal compressor overflow system thus eliminating the risk of refrigerant leakage to the atmosphere.
• The system renders full protection of the compressor even on increasing back pressure.
• The POV compressor overflow valve (main valve) has a very large capacity even with high back pressure when compared to direct operating back pressure independent pressure relief valves.
• Small dimensions mean easy handling and installation.
• Classification: DNV, CRN, BV, EAC etc. To get an updated list of certification on the products please contact your local Danfoss Sales Company.
AI183186419402en-001101
Compressor overflow valve, Type POV
Function
Pilot valve BSV 8
The pilot valve is actuated by the high pressure P1 and the back pressure P2”. The reference pressure in the stainless steel bellow (1) P0 is the atmospheric pressure. The e„ective area of the bellows is equivalent to the area of the valve seating, so the back pressure P2” does not a„ect the opening pressure of the valve.
Main valve POV
The main valve is of the normally closed (N.C.) type. The high pressure P1 acts on the valve inlet side of the valve cone (2). P1 pressure also passes through the piston rod (3) to the upper chamber (4) of the valve, acting on the top of the piston (5). The area of the piston is larger than the area of the valve seat and this together with the spring pressure keeps the valve closed.
System BSV 8 + POV
When the pressure P1 reaches the set pressure of the pilot valve, it starts opening. The pressure of the pilot line P2” and of the lower chamber (6) of the main valve increases. The pressure of the lower chamber is limited by flow through the nozzle (7). When the flow through the pilot valve exceeds the capacity of the nozzle, the pressure of the chamber (6) increases, providing the opening of the main valve. When the pressure P1 is reduced, the pilot valve closes, and the pressure P2” is equalized through the nozzle (7). The spring then closes the main valve. The closing time is ≤30 seconds.
Table 1: Function
fig. 1, Inactive system (closed valve) |
fig. 2, Active system (open valve) |
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Pilot valve |
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Pilot valve |
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BSV 8 |
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BSV 8 |
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Main valve |
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Main valve |
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POV |
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POV |
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To oil separator |
Condensing |
Evaporating |
From |
To oil separator |
Condensing |
Evaporating |
From |
condenser |
pressure |
pressure |
evaporator |
condenser |
pressure |
pressure |
evaporator |
Installation of compressor overflow valve POV + BSV
Set pressure
The BSV 8 set pressure is factory set in the range 15 25 bar(g) (145 363 psig), where 15 bar(g) is the minimum value for this application Figure 6: Capacity - POV 600.
Standard set pressures
18.0, 21.0, or 25.0 bar(g) (261, 305 or 363 psig). The operational pressure of the plant should be at least 15% below the set pressure of the pilot valve, and the opening pressure of the pilot valve (pset + 10%) must be below the reseating pressure of the safety valve protecting the plant. This implies a perfect operation of the plant.
Back pressure
P2-0 is the e„ective back pressure of the POV main valve P2-0 = P2-1 + ∆Poutlet where ∆Poutlet is the pressure loss in the outlet line of POV (2).
P2-1 Is normally equal to the evaporating pressure.
P2-0 must not exceed the limits in Figure 6: Capacity - POV 600.
Pressure loss in inlet line
© Danfoss | Climate Solutions | 2021.02 |
AI183186419402en-001101 | 2 |
Compressor overflow valve, Type POV
The pressure loss in the inlet line of the POV (1) will not a„ect the function of the POV + BSV system, but a high
pressure drop will reduce the capacity. If the pressure drop in the inlet line ΔPinlet exceed 3% of the opening pressure, the capacity reduction must be taken into consideration by calculation.
Pressure drop in the pilot inlet line
In order to ensure a proper function of the POV + BSV system, the pilot valve must be activated by the plant pressure. It is important that the inlet line of the pilot valve is mounted in a way which ensures that the pilot pressure is identical with the plant pressure. If the pilot pressure is mounted in the inlet line of the POV valve, it must be verified that the pressure drop in the pilot inlet line (3) ΔPinlet does not exceed 3% of the opening pressure.
Table 2: Installation of compressor
POV + BSV system |
Flow diagram |
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Plant |
Pressure |
Compressor |
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safe system |
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High pressure |
Figure 1: 3 |
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Pilot valve |
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Main valve |
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Set pressure |
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BSV 8 |
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POV 40 - 80 |
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on safety |
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valves (SFV) on |
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refrigerant plant |
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Max. opening |
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P2-0 |
e.g. oil separator |
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pressure of |
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POV + BSV |
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system |
P1-1 |
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Set pressure of |
Evaporating |
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pressure |
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pilot valve BSV |
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P2-1 |
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P1-0 |
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Operating |
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pressure on |
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Condensing |
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plant |
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pressure |
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Compressor |
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Low pressure
Figure 2: Fig. 4, range of application of BSV 8 POV
Max. back pressure bar(g) |
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Set pressure bar(g) |
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Important: When locating the inlet line to the pilot valve, it is important that the connection is mounted in the gas phase and not in an oil phase, if any.
•Pressure drop in the pilot outlet line
•The pressure loss in the BSV outlet line (4) ∆PP-outlet is not critical.
•Minimum internal diameter of the pilot outlet line 8 mm (0.314 in.)
•Maximum length of pilot outlet line 1 m (3.25 ft)
© Danfoss | Climate Solutions | 2021.02 |
AI183186419402en-001101 | 3 |
Compressor overflow valve, Type POV
Note: The guidelines mentioned above are securing a safe function of the POV + BSV system, but there might be restrictions from national authorities.
NOTE:
Valve type POV is categorized as a compressor overflow accessory (not as a safety accessory). Hence a safety valve (e.g. SFV) has to be installed to protect the system against excessive pressure.
Fig. 5 shows a typical application of the POV + BSV system. In the example a non return valve has been mounted in the suction line, as well as a shut-o„ valve in the pressure line. It is good practise and a demand from the authorities of most countries to mount a safety valve on the oil separator.
If the shut-o„ valve in the pressure line is closed, and aIl regulation equipment fails, the pressure after the compressor will rise, and the BSV + POV system is activated. Provided that the required motor e„ect is present, there will be a rise in temperature caused by the compression work, followed by a rise in pressure. Therefore, the safety relief valve of the oil separator must, besides being dimensioned for “normal” heat input, also be dimensioned for heat input, corresponding to the e„ect of the motor.
Figure 3: Installation of compressor overflow valve POV + BSV
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Compressor |
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Evaporating pressure |
Condensing |
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pressure |
Oil separator |
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© Danfoss | Climate Solutions | 2021.02 |
AI183186419402en-001101 | 4 |
Compressor overflow valve, Type POV
Media
Refrigerants
Applicable for the refrigerants HCFC, HFC, R717 (Ammonia), R744 (CO2). Flammable hydrocarbons are not recommended. For further information please contact your local Danfoss Sales Company
New refrigerants
Danfoss products are continually evaluated for use with new refrigerants depending on market requirements.
When a refrigerant is approved for use by Danfoss, it is added to the relevant portfolio, and the R number of the refrigerant (e.g. R513A) will be added to the technical data of the code number. Therefore, products for specific refrigerants are best checked at store.danfoss.com/en/, or by contacting your local Danfoss representative.
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AI183186419402en-001101 | 5 |
Compressor overflow valve, Type POV
Product specification
Pressure and temperature data
Table 3: Pressure and temperature data
Features |
Description |
Pressure setting range |
15 - 25 bar(g) (218 363 psig) |
Strength test |
50 bar(g) (725 psig) |
Leakage test |
25 bar(g) (363 psig) |
PB/MWP |
40 bar (580 psig) |
Temperature range |
–50/+150 °C (–58/+302 °F) |
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Design
Control/Identification
All pilot valves (BSV 8 Safety Relief Valves) are adjusted, tested and sealed before leaving Danfoss A/S. For that reason Danfoss can only guarantee correct operation, as long as the seal remains unbroken.
Transport/Handling
POV and BSV are supplied separately from Danfoss. BSV safety valves are fitted with special protection covers and packed in purpose made cartons. POV valves are provided with protection covers. It is important that the protective covers remain fitted until the valve is installed. To ensure the exact and precise operation of the valve it must be handled with care.
Re-calibration/servicing
In certain countries the authorities demand that the valves are readjusted at least once a year (see local rules).
Capacity
The design and construction of the compressor overflow valve has been tested and approved by TÜV. This test comprises control of the function of the valve as well as measuring of the capacity, which is the basis of the curves and tables on the following pages.
Installations
To ensure exact operation of the valve it should be installed with the spring housing upwards (refer to "Installation of compressor overflow valve POV + BSV" on the following pages).
When the valve is mounted, it is important to avoid the influence of static, dynamic and thermal stress.
Connections
Available with the following connections:
•Welding DIN (2448)
•Welding ANSI (B 36.10):
◦DN 40, Schedule 80
◦DN 65 - 80, Schedule 40
Figure 4: DIN
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