Data Sheet
Liquid level regulating valves
Type PMFL / PMFH and SV
For modulating liquid level control in refrigeration, freezing and air conditioning plant
For modulating liquid level control in refrigeration, freezing and air conditioning plant, a system comprising a liquid level regulating valve type PMFL or PMFH, controlled by a pilot €oat valve type SV, is used.
PMFL and SV systems are used on the evaporator side. PMFH and SV systems are used on the condenser side.
The system is suitable for use with ammonia or €uorinated refrigerants. The PMFL and PMFH can be used in liquid lines to or from
• evaporators
• separators
• intermediate coolers
• condensers
• receivers
Modulating liquid level regulation provides liquid injection that is proportional to the actual capacity. This gives a constant amount of €ashgas, thus ensuring stable regulation and economic operation because variations in pressure and temperature are held to a minimum.
AI242086443737en-001001
Liquid level regulating valves, Type PMFL / PMFH and SV
Features
•Applicable to HCFC, HFC and R717 (Ammonia)
•PMFL / PMFH are based on PM valve family housings
•Same €ange programme as for PM valve series
•Valve housing in low temperature cast iron (spherical) - EN GJS 400-18-LT
•Manual operation possible
•Position indicator available
•Pressure gauge connection to monitor inlet pressure
•Simple installation
•Main valve top cover can be located in any position without affecting the function
•Classification: DNV, CRN, BV, EAC etc. To get an updated list of certification on the products please contact your local Danfoss Sales Company
© Danfoss | Climate Solutions | 2021.02 |
AI242086443737en-001001 | 2 |
Liquid level regulating valves, Type PMFL / PMFH and SV
Functions
PMFL
Figure 1: PMFL
to SV float |
When the liquid level inside the €oat drops, the €oat orifice opens. This relieves the higher pressure, ps, acting on the servo piston to the low pressure side causing the PMFL to open. Variations in liquid level will result in variations in pressure over the piston and variation in the amount of liquid injected. It is important to choose the correct spring set when designing the plant. The spring set should be selected from the table below:
Table 1: Subcooling
Subcooling |
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Pressure di€erence over main valve |
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bar |
psi |
bar |
psi |
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K |
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F |
4 – 15 |
58 – 218 |
1.2 – 4.0 |
17 – 58 |
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0 |
– 8 |
0 – 14 |
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Normal spring set |
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Weak spring set |
8 |
– 40 |
14 – 72 |
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Strong spring set |
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The setting spindle, pos. 60, has not been set from factory. It is imperative that the setting spindle is adjusted before the valve is put into operation. The outer spring, pos. 23, is preset and the inner spring, pos. 43, is adjusted when turning the spindle. The following tables shows the adjustment of the inner spring in number of turns of the spindle as a function of valve size, spring type and pressure difference:
Table 2: PMFL
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C/w normal (factory mounted) spring set, subcooling 0 – 8 K ~ 0 – 14 F |
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PMFL |
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Pressure di€erence (Dp) over PMFL in bar or psi |
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< 5 bar |
5 – 8 bar |
8 – 10 bar |
10 – 12 bar |
> 12 bar |
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< 72 psi |
72 – 116 psi |
116 – 145 psi |
145 – 174 psi |
> 174 psi |
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80 |
No tension |
2 – 3 |
3 – 4.5 |
4.5 – 6 |
ca. 7 |
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125 |
No tension |
3 – 5 |
5 – 7 |
7 – 9 |
ca. 10 |
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200 |
No tension |
3 – 5 |
5 – 7 |
7 – 9 |
ca. 10 |
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300 |
No tension |
4 – 6 |
6 – 9 |
9 – 12 |
ca. 14 |
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Table 3: PMFL
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C/w strong spring set, subcooling 8 – 40 K ~ 14 – 72 F |
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PMFL |
Pressure di€erence (Dp) over PMFL in bar or psi |
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6 – 9 bar |
> 9 bar |
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87 – 131 psi |
> 131 psi |
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80 |
4 |
Max. tension |
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125 |
6 |
Max. tension |
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© Danfoss | Climate Solutions | 2021.02 |
AI242086443737en-001001 | 3 |
Liquid level regulating valves, Type PMFL / PMFH and SV
Table 4: PMFL
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C/w stong spring set, subcooling 8 – 40 K ~ 14 |
– 72 F |
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PMFL |
Pressure di€erence (Dp) over PMFL in bar or psi |
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6 – 16 bar |
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87 – 232 psi |
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300 |
Spring must always be set to max. tension |
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Table 5: PMFL
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C/w weak spring set, low pressure plants |
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PMFL |
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Pressure di€erence (Dp) over PMFL in bar or psi |
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1.2 – 1.8 bar |
1.8 – 2.5 bar |
2.5 – 3 bar |
3 – 4 bar |
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17 – 26 psi |
26 – 36 psi |
36 – 43 psi |
43 – 58 psi |
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80 |
No tension |
3 – 4 |
4 – 6 |
Max. tension |
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125 |
No tension |
4 – 6 |
6 – 8 |
Max. tension |
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200 |
No tension |
4 – 6 |
6 – 8 |
Max. tension |
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300 |
No tension |
5 – 7 |
5 – 7 |
Max. tension |
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Figure 2: PMFL function example
From compressor |
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To compressor |
From evaporator |
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Condenser |
Alarm |
Alarm |
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float switch |
Overflow |
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valve |
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Liquid level |
Through type receiver |
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Filter |
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Oil drain |
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valve |
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To evaporator |
The values for spindle turns are an indication for an initial setting only. If a position indicator is used, a more precise modulation can be achieved when fine tuning the valve setting. If the PMFL is not opening fully, the spring tension must be reduced. If the PMFL is operating in a ON / OFF function, the spring tension should be increased. The condenser pressure will have an effect on the fine tuning and large variations in condensing pressure might call for readjustment. The subcooling is measured just before the PMFL and the pressure difference is for the valve only excluding piping and armatures.
The PMFL can be used together with SV 4 as a pilot valve.
The orifices determines the Kv (Cv) value of the pilot and the following table can be used as an initial selection guide:
© Danfoss | Climate Solutions | 2021.02 |
AI242086443737en-001001 | 4 |
Liquid level regulating valves, Type PMFL / PMFH and SV
Table 6: PMFL
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PMFL |
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SV 4 – 6 |
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Ø 2.5 |
Ø 3 (SV 4) |
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80 |
X |
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125 |
X |
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200 |
X |
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300 |
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X |
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The final choice of orifice may vary depending on refrigerant and pressure levels. Smaller pressure levels needs a bigger orifice. Pressure difference levels below 3 bar (43 psi) need SV 4 – 6 with Ø3 mm orifice.
SV floats for PMFL
SV 4 can be used for PMFL low pressure control system. The €oat must be connected as shown.
Figure 3: SV floats for PMFL
Inlet to SV 4 from PMFL |
NOTE:
Only one inlet connection possible for SV 4.
PMFH
Figure 4: PMFH
If the liquid level inside the SV €oat rises, the €oat orifice opens and relieves pressure through the pilot line to the top of the PMFH, increasing the pressure, ps, moving the pushrod downwards and opening the PMFH. The pilot line is connected in the topcover at SI. Override of the pilot signal can be made by using an EVM valve at SII. It is important to choose the correct spring set when designing the plant. The spring set should be selected from the table below:
© Danfoss | Climate Solutions | 2021.02 |
AI242086443737en-001001 | 5 |
Liquid level regulating valves, Type PMFL / PMFH and SV
Table 7: spring set selection
Pressure di€erence over main valve
bar |
psi |
bar |
psi |
0 – 4.5 |
0 – 65 |
> 4.5 |
> 65 |
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Weak spring set |
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Normal spring set |
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The PMFH can be used together with either SV 1 or 3 with the SV mounted with the bleed valve downwards, refer to the drawing below. This reverses the opening so that rising €oat opens the orifice.
Figure 5: PMFH function example
From low stage |
Tohigh stage |
compressor(s) |
compressor(s) |
Alarm
Alarm float switch
S-connection
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Intermediate |
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pressure |
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To |
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vessel |
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low stage |
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separator |
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P-connection
From high stage compressor(s) 
Condenser
SV 3 (1)
Liquid trap receiver
Filter 
To 
compressor cooling 
NOTE:
High pressure €oat system (for explanatory purposes only)
SV 1 - 3
SV 1 – 3 €oat has 2 different pilot connections: S-port (series connection with PMFH) or P-port (parallel connection with the PMFH).
P-port:
When using the P-port, it is possible to force open the PMFH valve to a fully open position. This is practical for service purposes or to confirm if the €oat has su‡cient capacity for the PMFH and the operating conditions. However, when P-port connection is used it is possible to overfill a system due to constant bleeding or unautorised tampering. In this case, it is advisable to introduce a shut off when the liquid level reaches a preset point. Shut off can be done via an electrical switch if an EVM valve is mounted in the SII port in the top of the PMFH. It is only advisable to use the P-port at low pressure difference.
S-port:
The S-port offers the advantage of a preorifice which divides the pressure drop and any wear possibility due to cavitation. S-port connection must be used at high pressure differences, dp > 10 bar (145 psi). The Kv (Cv) value of the SV is higher using P-port than using S-port. A higher P-band can thus be obtained.
© Danfoss | Climate Solutions | 2021.02 |
AI242086443737en-001001 | 6 |
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