The remote seal also referred to as diaphragm seal are connected to a measuring instrument using a direct connection or a capillary.
A remote seal system consists of an external sensing diaphragm mounted to the process and connected to a differential pressure transmitter with oil-filled capillaries. The capillaries and seals are filled with incompressible oil suited with process pressure and temperature. The transmitter may be mounted at a certain distance or nearby the high-pressure process connection.
For transmitters under vacuum are mounted below the high-pressure side tap to reduce the effects on the transmitter fill fluid.
Advantages of the remote seal capillary transmitters:
- Plugging caused by viscous processes and suspended solids with piped impulse lines can be overcome with capillary seals.
- Capillary systems are most flexible and not rigid like piped impulse lines.
- As Capillary system makes it possible to easily install around permanent structures, confined spaces.
- Transmitters can be mounted at a certain safe distance from the process pipelines or tanks.
- Remote capillary Transmitter mounted at zero levels.
- Remote capillary transmitter mounted below the seals
- Remote capillary Transmitter mounted above the top seals.
- Remote capillary transmitter between the seals.
- Remote capillary transmitter mounted below the seals on the Closed Tank.
- Remote capillary transmitter mounted on the Closed Tank.
1.Remote capillary Transmitter mounted at zero levels.

Hd = Vertical distance from the transmitter to high-pressure seal
Ld = Vertical distance from the transmitter to low-pressure seal
Lmax = The maximum process level above the high-pressure seal.
Lmin = The minimum process level above the high-pressure seal.
Sf = Specific gravity of remote fill fluid
Sp = Specific gravity of process fluid
Tank span = Lmax *Sp – Lmin * Sp
= (100 in.* 0.55) – 0 in*0.55) = 55 inH2O.
4 mA = Lmin *Sp + Hd *Sf
= (0 in.* 0.55) + (0 in.* 01.09) = 0 inH2O
20 mA = Lmax * Sp + Hd * Sf
= (100 in.* 0.55) + (0 in.* 01.09) = 55 inH2O
Span = 55 inH2O (55 to 0 inH2O)
Note: Both of the installations would have the same calculated range points.
Note: Silicone 704 has a specific gravity of 01.09.
2.Remote capillary transmitter mounted below the seals.

Tank span = Lmax* Sp – Lmin * Sp
= (100 in.* 0.55) – (0in *.55 in) = 55 In H2o
4 mA = Lmin *Sp + (Hd* Sf)
= (0 in.* 0.55) + (60 in.* 01.09) = 65.4 inH2O
20 mA = Lmax *Sp + (Hd *Sf)
= (100 in* 0.55) + (65.4) = 120.4 inH2O
Span = 55 inH2O (120.4 to 65.4 inH2O)
Note: Silicone 704 has a specific gravity of 01.09.
3 . Remote capillary Transmitter mounted above the top seal

Tank span= Lmax Sp – Lmin* Sp
= (100 in. 0.55) = 55 inH2O
4 mA = Lmin * Sp +(Hd * Sf)
= (0 in * 0.55) + (-120 in * 01.09) = –130.8 inH2O
20 mA = Lmax * Sp + (Hd * Sf)
= (100 in * 0.55) + (-120 in.* 01.09) = –75.8 inH2O
Span = 55 inH2O (–130.8 to –75.8 inH2O)
4. Remote capillary transmitter between the seals.

Tank span = Lmax SG
= 100 in. 0.55 = 55 inH2O
4 mA = Lmin *Sp – (Ld* Sf) +(Hd * Sf)
= (0 in. 0.55) – (60 in.* 01.09) + (– 60 in.* 01.09) = –130.8 inH2O
20 mA = Lmax * Sp – (Ld * Sf) +(Hd Sf)
= (100 in. 0.55) – (60 in. 01.09) + (–60 in. 01.09) = –75.8 inH2O
Span = 55 inH2O (–130.8 to –75.8 inH2O)
Note: Silicone 704 has a specific gravity of 01.09.
5. Remote capillary transmitter mounted below the seals on the Closed Tank

Tank span= Lmax *SG
= (100 in.* 0.55) = 55 inH2O
4 mA = Lmin * Sp – (Ld * Sf)+ (Hd+Sf)
= (0 in.* 0.55) – (120 in.* 01.09) + (60in * 1.09) = – 130.8 inH2O
20 mA = Lmax *Sp – (Ld* Sf) + (Hd+Sf)
= (100 in.* 0.55) – (120 in.* 01.09) + (60in * 1.09) = –75.8 inH2O
Span = 55 inH2O (–130.8 to –75.8 inH2O)
Note: Silicone 704 has a specific gravity of 01.09.
- Remote capillary for closed Tank

Tank span= Lmax *Sp – Lmin* Sp
= (100 in.* 0.55) = 55 inH2O
4 mA = Lmin * Sp – (Ld * Sf)
= (0 in.* 0.55) – (120 in.* 01.09) = – 130.8 inH2O
20 mA = Lmax *Sp – (Ld* Sf)
= (100 in.* 0.55) – (120 in.* 01.09) + (60in * 1.09) = –75.8 inH2O
Span = 55 inH2O (–130.8 to –75.8 inH2O)
Note: Silicone 704 has a specific gravity of 01.09.
Author: PSS Bapu Rao
Source: Emerson
Various calculations are made easy to understand.