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Series-251-253-254
Welded Chamber Liquid Level Control, 1250 psig, Hermetic Switches
- Welded-steel chamber rated 1250 psi @ 100 °F, 750 psi @ 750 °F for high-pressure / high-temp service
- Handles fluids to 0.60 SG with 1″ NPT or flanged side/bottom connections for easy mounting
- Stainless float with magnetic actuation offers smooth, reliable level switching
- SPST, SPDT, or DPDT switch options with general, weather, or explosion-proof enclosures
Series-251-253-254
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Product Overview
The Series-251-253-254 Welded-Chamber Level Control from Dwyer combines rugged construction with flexibility for demanding applications in the process industries. Designed for maximum reliability, these units feature a heavy welded carbon-steel (or optional 316-SS) chamber engineered to withstand extreme conditions - up to 1,250 psi at 100 °F and service temperatures up to 750 °F.
This family supports a variety of installation configurations: the 251 model uses a combination 1″ NPT/socket weld hub (horizontal plus vertical), the 253 offers one vertical and one horizontal flanged connection, and the 254 uses two vertical flanged connections. This flexibility in mounting makes the series ideal for retrofits or complex vessel geometry.
The sensing mechanism includes a stainless-steel float assembly and magnetic actuator head which operates without internal magnet accumulation—a design feature that reduces maintenance and improves long-term reliability. The series is available with a wide array of switch options (SPST, SPDT, DPDT) and contact types (mercury, snap-action, hermetically sealed), enabling integration into general, weather-proof or explosion-proof environments.
With minimum specific gravity ratings as low as 0.60 for some flange-mounted variants, the Series-251-253-254 is suitable for light liquid applications and challenging fluid services. The robust materials, high pressure/temperature capability, and flexible switch/enclosure options make this level control ideal for refiners, chemical plants, power generation facilities, tanks, vessels and other critical fluid systems.
Show Ratings & Reviews
| EXAMPLE | 251 | WT | 7810 | C1 | 60 | 251-WT-7810-C1-60 Liquid Level Control, welded carbon steel chamber, weatherproof enclosure, SPDT snap switch, fixed deadband, automatic reset, operating pressure 350 psig (24 bar) at 100°F (38°C), 300 psig (21 bar) at 600°F (315400°C), side/bottom 1" NPT, minimum specific gravity 0.60. | |
| CONNECTION | 251 | One Vertical and One Horizontal 1" NPT | |||||
| 253 | One Vertical and One Horizontal Flanged Connection | ||||||
| 254 | Two Vertical Flanged Connections | ||||||
| ENCLOSURE | G | General Purpose, NEMA 1 | |||||
| WT | Weatherproof, NEMA 3R, 4, 4X | ||||||
| E | Explosion-proof, NEMA 7, 9, Class I Groups B, C, D, Class II Groups E, F, G | ||||||
| EV | Explosion-proof/Vapor-proof, NEMA 7, 9, Class I Groups B, C, D, Class II Groups E, F, G | ||||||
| CIRCUITS (for electrical circuits see charts A & B below) |
48XX | Single Stage Mercury Switch, see chart A | |||||
| 48XX-XX | Two Stage, Mercury Switch, see chart A | ||||||
| 78XX | Single Stage, Snap Switch, see chart B | ||||||
| 78XX-XX | Two Stage, Snap Switch, see chart B | ||||||
| 98XX | Single Stage, High Capacity DC Snap Switch, use heat fins (HF) if process temperature exceeds 350°F (177°C), do not exceed 450°F (232°C), see chart B | ||||||
| 98XX-XX | Two Stage, High Capacity DC Snap Switch, use heat fins (HF) if process temperature exceeds 350°F (177°C), do not exceed 450°F (232°C), see chart B | ||||||
| CHAMBER MATERIAL | C1 | Carbon Steel Body | |||||
| HFC1 | Heat Fins, Carbon Steel Body | ||||||
| C216 | 316SS Body | ||||||
| HFC216 | Heat Fins, 316SS Body (251 only) | ||||||
| C217 | 316SS Housing with Shield (251 only) | ||||||
| MINIMUM SPECIFIC GRAVITY |
60 | 0.60 Specific Gravity (251 only) | |||||
| 75 | 0.75 Specific Gravity (251 only) | ||||||
| 160 | 0.60 Specific Gravity & 150# Flange (253, 254 only) | ||||||
| 175 | 0.75 Specific Gravity & 150# Flange (253, 254 only) | ||||||
| 360 | 0.60 Specific Gravity & 300# Flange (253, 254 only) | ||||||
| 375 | 0.75 Specific Gravity & 300# Flange (253, 254 only) | ||||||
| 660 | 0.60 Specific Gravity & 600# Flange (253, 254 only) | ||||||
| 675 | 0.75 Specific Gravity & 600# Flange (253, 254 only) | ||||||
| OPTIONS | STW | SS Tag Wired | |||||
| 01 | Breather Only (E-Housing only) | ||||||
| 02 | Drain Only (E-Housing only) | ||||||
| 12 | Breather & Drain (E-Housing only) | ||||||
| 23720 | Fungus Proofing |
CHARTS A & B - ELECTRICAL CIRCUITS AND RATINGS
| SWITCH TYPE | SWITCH ACTION | ELECTRICAL RATINGS IN AMPS | ORDERING CODE | |||||||
| AC | DC | SINGLE STAGE | TWO STAGE | |||||||
| 120V | 240V | 440V | 30V | 125V | 250V | LOWER | UPPER | |||
| CHART A Mercury Contacts |
SP-ST open on level FALL | 10 | 5 | 3† | 10 | 5 | -4821 | -4821 | -21 | |
| SP-ST open on level RISE | 10 | 5 | 3† | 10 | 5 | -4820 | -4820 | -20 | ||
| SP-DT one switch | 4 | 2 | 1† | 4 | 2 | -4810 | -4810 | -10 | ||
| SP-DT two switches E.I.* | 10 | 5 | 3† | 10 | 5 | -4815 | -4815 | -15 | ||
| DP-ST two switches E.I.* open on level FALL | 10 | 5 | 3† | 10 | 5 | -4813 | -4813 | -13 | ||
| DP-ST two switches E.I.* open on level RISE | 10 | 5 | 3† | 10 | 5 | -4814 | -4814 | -14 | ||
| DP-DT two SP-DT switches | 4 | 2 | 1† | 4 | 2 | -4806 | -4806 | -06 | ||
| CHART B snap action contacts |
SP-DT one switch | 12 | 5 | 3† | 0.5** | 0.25** | -7810 | -7810 | -10 | |
| DP-DT two SP-DT switches | 12 | 5 | 3† | 0.5** | 0.25** | -7806 | -7806 | -06 | ||
| SP-DT one hermetically sealed switch | 5 | 5 | 5** | -7810HM | -7810HM | -10HM | ||||
| DP-DT two hermetically sealed SP-DT switches | 5 | 5 | 5** | -7806HM | -7806HM | -06HM | ||||
| DP-DT two SP-DT switches | 10 | 3 | 10‡ | 3‡ | -9806 | -9806 | -06 | |||
| SP-DT one switch | 10 | 3 | 10‡ | 3‡ | -9810 | -9810 | -10 | |||
| DP-DT Two SP-DT switches | 2 | 2 | 0.4** | 0.25** | -1006 | -1006 | -06 | |||
| SP-DT one switch | 2 | 2 | 0.4** | 0.25** | -1010 | -1010 | -10 | |||
†Available on special order, change 1st digit in ordering code from 4 to 5 or 7 to 8, i.e., -4820 becomes -5820, -7810 becomes -8810, etc.
‡10 amp inductive (polarized) at 125 VDC.
*Electrically Independent.
**Resistive.