As a supplier specializing in API 610 pumps, I get a lot of questions from refinery engineers, plant maintenance managers, and pump designers about what makes these pumps so unique—especially when it comes to sealing. API 610 isn’t just a set of arbitrary rules; it’s a standard built to solve the most common, costly problems in heavy-duty process pumping: leaks, unplanned downtime, and safety risks. Over 12 years in this business, I’ve seen firsthand how cutting corners on sealing requirements can shut down a crude unit for days, or even lead to hazardous spills in volatile service. That’s why I want to break down the sealing requirements for API 610 pumps clearly, from the mandatory design specs to the real-world adjustments that our team at [Our Company] makes to ensure every pump we ship meets and exceeds these standards. API610 Pump
First, let’s start with the basics: API 610 is the American Petroleum Institute’s standard for centrifugal pumps in petroleum, chemical, and gas industry services, specifically designed for heavy-duty, continuous operation. Sealing is a make-or-break component here, because these pumps handle everything from crude oil and corrosive chemicals to high-temperature hydrocarbons. A failed seal isn’t just a maintenance hassle—it’s a safety hazard, a regulatory headache, and a major hit to production. So what does API 610 actually mandate when it comes to sealing?
Let’s start with the core sealing types allowed by the standard. API 610 doesn’t require a one-size-fits-all seal, but it does specify that you have two primary options: mechanical seals (the most common for API 610 pumps) and packed glands (only permitted for specific low-risk, low-pressure, low-temperature services). I’ll break those down, because the line between when each is allowed is critical.
Packed glands, for example, are not a default choice in API 610. The standard explicitly states that packed glands may only be used if the pump is for “non-hazardous service, operating at pressures not exceeding 1.6 MPa (16 bar), and temperatures not exceeding 200°C (392°F).” Even then, there are strict rules for the packing itself. It has to be a minimum of 12.7 mm (0.5 inch) square, made of a material compatible with the pumped fluid, and arranged in at least three rings with a split ring that has the gap offset 120 degrees between each ring. Also, API 610 requires that packed glands have a lantern ring (a port to introduce flush or seal fluid) located at the midpoint of the packing set. That’s non-negotiable—no lantern ring means the packed gland is out of compliance for most API services. I’ve had customers come to us asking to skip the lantern ring for a cheaper packed seal, but that’s a quick way to get excessive leakage, which violates both API standards and plant environmental rules.
Mechanical seals, on the other hand, are the go-to for almost all API 610 pumps, and the standard has a ton of specific requirements for these. First, API 610 mandates that every mechanical seal assembly for pumps above 37 kW (50 hp) must be a dual seals arrangement if the pump is handling hazardous fluids, operating above 2.2 MPa (22 bar), or at temperatures above 200°C (392°F). Wait, let me clarify that: dual seals aren’t the only option, but they’re required under those conditions. A single seal is only approved for lower-risk service, but even then, it has to meet specific design specs.
For single mechanical seals, API 610 requires that the seal faces are made of compatible materials—hard face on one side, soft on the other, with a hardness difference of at least 30 HRC to prevent scuffing. The hard face is usually tungsten carbide or silicon carbide, and the soft face is typically carbon graphite. The standard also requires that the seal chamber has a specific pressure differential: the seal chamber pressure should be between 0.05 MPa (0.5 bar) above suction pressure and the suction pressure plus 0.7 MPa (7 bar), unless external flush or seal gas is used to adjust it. That’s important because if the chamber pressure is too low, air can leak in, causing cavitation; if it’s too high, the seal faces will wear out too fast.
Dual mechanical seals, which API 610 requires for most high-risk services, have their own set of rules. The space between the two seals (called the seal cavity) has to be designed to circulate a buffer or seal fluid continuously. API 610 specifies that this cavity must have a pressure that’s slightly higher than the pumped fluid pressure to prevent any process fluid from leaking out into the environment. That means we have to size the seal flush system correctly—usually a filtered flush from the pump’s discharge line or a dedicated seal fluid system—to maintain that pressure difference. Also, dual seals require a seal fluid supply with a pressure gauge and a flow indicator, so plant operators can monitor if the flush is working. I can’t tell you how many times we’ve retrofitted pumps for customers whose old dual seals failed because they skipped the flow monitoring part; API 610 makes that mandatory for a reason.
Another key sealing requirement in API 610 is the provision for seal support systems. The standard doesn’t just talk about the seal itself—it lays out rules for the entire system that supports the seal. For mechanical seals, especially dual seals, you need a seal support system that can provide clean, compatible fluid to the seal cavity. API 610 requires that this system include a filter with a minimum 10 micron rating, a pressure regulating valve, and a temperature control device (like a heat exchanger) to keep the seal fluid within a specific temperature range—usually between 20°C and 80°C (68°F and 176°F) for most services. Why is that? If the seal fluid is too hot, it can break down, leading to seal face damage; if it’s too cold, viscous fluid won’t circulate properly, causing dry running which ruins seals in minutes.
Also, API 610 mandates that all seal connections (the ports for flush, vent, drain, and seal fluid) have to be sized for the flow rate required by the seal assembly. For example, a 50 hp API 610 pump with a single mechanical seal needs a 1/2-inch NPT port for flush, while a dual seal needs a 3/4-inch port for the seal fluid return. We always make sure to include these ports as standard on our pumps, because modifying a pump after delivery to add seal ports is not only time-consuming but often leads to leaks at the connection points.
One of the most overlooked sealing requirements in API 610 is the seal chamber design itself. The standard has specific dimensions for the seal chamber to ensure that the seal is properly aligned and has enough space for circulation. For example, the seal chamber bore must be within a specific tolerance relative to the shaft, usually H7 for the bore and h6 for the shaft, to prevent misalignment that can cause seal face wear. Also, API 610 requires that the seal chamber has a maximum length, because if it’s too long, the packing or seal can shift during operation, leading to leakage. Our engineering team does a full dimensional check of every pump’s seal chamber before it leaves our facility, because even a 0.1 mm misalignment can shorten seal life by 50% or more.
Another point: API 610 has requirements for leakage rates. For mechanical seals, the maximum allowable leakage is 5 mL per hour for clean, non-hazardous fluid, and 1 mL per hour for hazardous fluid. That’s a tiny amount, but it’s critical for safety and compliance. Packed glands have a higher allowable leakage—up to 10 mL per hour for non-hazardous service—but again, that’s only allowed in specific cases. We test every mechanical seal assembly on our API 610 pumps before shipping to ensure it meets this leakage rate; we’ve had customers reject pumps from other suppliers because their seals leaked 20 mL per hour, which is a violation of API 610.
Now, let’s talk about real-world service adjustments, because not all API 610 applications are the same. For example, if you’re pumping high-temperature fluids (over 300°C, or 572°F) like molten sulfur or heavy crude, API 610 recommends using a dual seal with a quench system to keep the seal faces cool. The quench fluid is usually water or a compatible hydrocarbon, introduced to the seal faces to prevent thermal distortion. Our team at [Our Company] adds this quench system as an option for customers handling high-temp services, because even if a seal meets API 610’s design specs, extreme temperatures will degrade it without additional cooling.
For corrosive services, like pumping hydrochloric acid or sulfuric acid, API 610 requires that the seal materials are corrosion-resistant. That means we have to use silicon carbide seal faces and Hastelloy or Alloy C-276 for the seal housing, instead of standard carbon steel. We don’t cut corners here—using lower-cost stainless steel for seal parts in corrosive service will lead to seal failure within a few weeks, which is way more expensive upfront than using the right materials.
Also, API 610 has specific requirements for pump operation that tie into sealing. For example, the pump’s minimum continuous stable flow (MCSF) is important because if a pump runs below MCSF, the fluid in the seal chamber won’t circulate, leading to overheating and seal failure. That means we have to communicate the MCSF to our customers along with the pump, because even a perfect seal will fail if the pump is run at too low a flow rate. We always include a flow curve with every pump shipment that shows the MCSF, so plant operators can avoid that common mistake.
I’ve seen too many pump manufacturers sell a pump that “meets API 610” but cuts corners on the sealing details, and that leads to headaches for their customers. At [Our Company], we go beyond the minimum requirements because we know that for process pumps, uptime is everything. For example, we offer an optional seal condition monitoring system for API 610 pumps, which uses sensors to track seal temperature, pressure, and leakage in real time. This isn’t required by API 610, but it gives plant maintenance teams a heads-up that a seal is starting to fail, so they can schedule a replacement during a planned shutdown instead of an emergency. That’s the difference between a supplier who just sells a product and one who partners with their customers to keep their operations running.
Now, let’s address a common misconception: some people think API 610 sealing requirements are just for new pumps, but they also apply to repairs and retrofits. If you’re replacing a seal on an existing API 610 pump, you have to use a seal that meets the same API 610 specs as the original. That means you can’t just buy a standard mechanical seal off the shelf; it has to be sized for your pump’s shaft diameter, seal chamber dimensions, and operating conditions. We provide seal replacement kits that are pre-tested to meet API 610 requirements, so our customers don’t have to guess which seal will work.
Another point for buyers: when you specify API 610 pumps, make sure you clearly define the service conditions for sealing. If you’re handling hazardous fluid, you need to specify that you require dual seals, not single. If you’re pumping high-temperature fluid, mention that you need a quench system. A lot of time, we get inquiries where customers just say “API 610 pump” without any service details, and we have to follow up to make sure we’re providing a pump that meets their sealing needs. That communication is key—API 610 sets the baseline, but your specific operating conditions will determine if you need additional sealing features.
I’ve talked to plant managers who’ve spent $50,000 on a pump from a supplier that said it meets API 610, only to have the seal fail three months later because the supplier used a single seal in a hazardous service. That’s a bad experience, and it’s avoidable. At our facility, every pump undergoes a full seal inspection during manufacturing: we check the seal face material, the seal chamber dimensions, the seal support system connections, and we perform a hydrostatic test on the seal cavity to make sure there are no leaks. We also run a performance test on every pump, which includes checking seal leakage and pressure, to confirm it meets API 610 requirements.
So to sum up the key sealing requirements for API 610 pumps, in order of importance: first, choose the right seal type (single or dual) based on service, pressure, and temperature. Second, ensure seal materials are compatible with the pumped fluid. Third, design and test the seal chamber and seal support system to API 610’s dimensional and pressure specs. Fourth, monitor leakage rates to stay within the standard’s limits. Fifth, account for real-world operating conditions, like temperature and flow, to prevent premature seal failure.
If you’re in the market for API 610 pumps and you want to make sure you’re getting ones that meet all these sealing requirements, we’re here to help. Our team has decades of experience working with refineries, chemical plants, and power plants to deliver pumps that are reliable, safe, and compliant with API standards. Whether you need new pumps, seal replacements, or guidance on sealing for your existing equipment, you can reach out to our team to discuss your specific needs.
Multistage Centrifugal Pump References
API Standard 610, Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries, 11th Edition, American Petroleum Institute, 2011.
Pump Sealing Technology: A Guide for Industrial Applications, Hydraulic Institute, 2019.
“Sealing Requirements for Heavy-Duty Process Pumps”, Process Safety Progress, Vol. 35, No. 2, 2016.
Hunan Sanchang Pump Co., Ltd.
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Address: No.517, Xiangfu East Road, Yuhua District, Changsha City Hunan
E-mail: info@sanchangpump.net
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